...to fall in love with providers.  That's one less problem they have to deal with.

 
Also, if you're married they think you're "safe."  If another woman has married you and has been living with you, then you're probably not a serial killer (although a few serial killers have been married and led seemingly normal lives).  OTOH, single guys are more likely to be stalkers.

 
Or maybe you just have that henpecked look of a guy who's been nagged by a shrew of a wife for twenty years.  

I imagine they are curious.  I actually don't mind questions like that.  I actually think they feel more comfortable with married guys (even if they might look down on it) for the same reason companies used to prefer to hire married guys ... marriage demonstrates some small measure of character stability.
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But mainly I think they are just curious.  It's also something to chit chat about.
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That said I don't actually recall being asked about it.  But I don't tend to remember chit chat.

there seem to be some consistent patterns.  Blackmail has never entered my mind, but I think there are three legit reasons to ask. . . . .

1.   To assess your spending potential.   Typically, single guys have more freedom to spend time with a provider and can usually do longer sessions, overnights and travel if they have the financial depth.  There are married guys that do this stuff too, so there are always exceptions.  OTOH, many married guys have more limited budgets because its sometimes hard to hide money from the wife.  

 
2.  If you're married, many providers assume (often wrongly) that SOME of your sexual needs are being fulfilled by your wife.  Single guys, all else being equal, will usually hobby more often than married guys unless they have an SO at the time.  If you are single, they  may be sizing you up for an arrangement of some type, i.e. Sugar-dad, where they rely on a set monthly stipend.  There are many married guys who play in the sugar bowl, too, but again, scheduling is often an issue for married guys that limits the amount of time they can spend with a SB.  

 
3.  Older providers are often thinking about retirement, which requires an exit strategy.   If they think you can afford them full time, then yes, they may be sizing you up for long-term (marriage?) potential.  

 
Unless you are bottom-feeding with low-end hookers, I don't think you need to assume there is anything nefarious going on.  They are just "qualifying" you the way any salesperson would to assess how much you might be food for.  Along with the marriage question, they will usually ask about your profession, whether you have a girlfriend, children, etc.  They all have a bearing on how much they  think they can count on in the future from your  patronage, assuming you will repeat.  

for all the cases you suggested and all the ones you didn't think about.

That doesn't mean that the ones asking you are looking to blackmail you.

In my case I have near certain views that they are asking to make some conversation and just out of interest (without any judgement or personal interests) or because they find me attractive and interesting enough to perhaps think about some type of RL relationship.

Don't make too much of it and certainly feel free to answer in any way you wish -- the time spent, at least initially, is all about creating the image of intimacy and/or passion. 100% honesty is not required or even expected (and often really not wanted).

I try not to read much into it. Just a piece of conversation...  
if anything married people may be less risky because they have more to lose than a single guy, ceteris paribus.

Interesting question because I’ve always wondered why men always ask me my age. I look a certain age so why ask for the exact number? My conclusion, they’ve just run out of topics of conversation. I was taught a gentleman never asks a lady her age and I guess being behind closed doors a lady shouldn’t make certain inquiries regarding a gentleman she’s keeping company with. Moral of the story, as time marches on acceptable norms change. Live and let live !

....so what's one more? :P

find it interesting that they ask.  I am almost always asked.  It does not bother me but it does strike me as odd, I never ask a personal question of a provider and quite often you will see a provider on here complain about guys asking personal questions.  It is interesting to me that they would ask a question that they themselves would not want to be asked.  I'm always tempted to say no I'm not married, how about you?, but I never do

They don't have to ask.   They understand why I came to see them, I'm there for some strange.

Providers are more likely to say, “You are married, right?” I don’t know what to make of it or given it much thought.  Maybe I have an air of sexual desperation typically found with married men.  😳

I get asked this question, now that I read about it, just about everytime too. Never really worried about it or thought anything from it. I give a different response based on my read of the ASP. If you enjoyed your time, you will visit again, but many no desire for another visit. Usually they will tell me they are looking for regular, repeat clients.

Cuz you're so fucking good looking

They don't want your pig of a wife to go chase them down and kill them!

Seriously. It's none of their fucking business unless you want it to be.

If you're one of those whiny fuckers that bitch and moan how your old lady doesn't fuck you anymore, blah, fucking blah, stick your dick in their mouth.  

Done

You're paying for their time. Whether you get nekkid or not you're on the clock.  

Bust your nut and get the fuck out...

I'll admit  I was friends with some cuz I'm a cool guy. But if you have to ask, yeah....  

a client if he is married. It is none of my business.  
Many clients share on their own that they are married and quite a bit of times discuss issues they are experiencing in their marriage. Not sure why you are being asked this more often than not.Maybe they are just making small talk.
Funny I do not ask gents about their dating/married life but I have had quite a bit of clients ask about mine.

I agree with the "exit strategy" idea. This question is asked by almost every massage parlor girl for obviously the same reason.

When providers ask if I am married I tell them that my wife passed away in the past year.

They seem to be more affectionate with more hugging and DFK and ask "is there anything that your wife did that can do?"

To which I say "BBBJ" After she starts I then say "with CIMSW".  

Most realize that it is a joke - some redouble their effort.