Well they've climaxed so generally the whole concept of the meet is over and all they are left with is the cold light of day. Although some like to go again.
A little like when I watch porn, as soon as I have cum I'm like ewwww get rid of these off my screen. 
Over the years I've noticed something consistent with men, they treat you like you are the most important woman in world when they need their balls emptying.. it's only after they are empty and how they behave/treat you,  you really can see how they really feel about you!
I've had some guys actually say to me after.. ahhh I hate this bit; it's fascinating watching them be so uncomfortable and awkward; I just say I can go if you want me too? I mean to me a guy asking me to go early on full pay is not something I have a problem with at all

A while back I posted something similar to this. It used to upset me somewhat when (just as you describe!) they treat you as the sexiest creature they have ever met but once the deed is over they can hardly look at or talk to you.  I still find it rude but accept it and don't take it personally.

It's that same stereotype of the man that rolls over after sex and goes to sleep! Same principle I guess. When I started I was really surprised that someone who had paid for half an hour and was done after 15 to 20  mins was more than happy to leave. I thought they would want they whole time, using the rest for chatting or something but I know better now!

I suppose there are some who once they cum they feel guilty either for cheating, spending the money or whatever, like a comedown after the high. I have often seen guys go a bit moody or uncommunicative afterwards, it's very normal, just smile and escort them out the door...

I've had a guy see me a couple of times.
Arrives fairly quiet and a bit shy, but as soon as he comes, he goes the opposite way, his personality comes out in full, makes the odd joke, whilst smiling and even asks about my availability, for when he is wanting to see me again.
A few times, he has had me laughing with him, as he  is a very polite guy to be with, just a bit shy on arrival and quiet in the time whilst getting intimate.

I've had a guy see me a couple of times.
Arrives fairly quiet and a bit shy, but as soon as he comes, he goes the opposite way, his personality comes out in full, makes the odd joke, whilst smiling and even asks about my availability, for when he is wanting to see me again.
A few times, he has had me laughing with him, as he  is a very polite guy to be with, just a bit shy on arrival and quiet in the time whilst getting intimate.

Yes I have met men like this too. The opposite to the ones who go quiet and distant.

Back to the silent and distant ones though and I have heard myself making small banal talk just to break the silence and one day I vowed to myself I would no longer do this as if they can't be polite enough to be pleasant after they have cum then why the hell should I?

So now I tend to go as dead as them. I leave them to dress alone or just sit on the bed and observe them.

Many are fine though and are almost as friendly as before sex so it is not a big problem.

It's been very rare this happened to me but it's always been with younger guys.

The worst one was when he booked an hour and finished in 10 minutes and very obviously wasn't going to go again.  I could just tell he was lying there thinking "can I ask for a partial refund" and I wasn't having any of that. I wittered on about food (my favourite topic) for about 10 mins then turned to him and said "so what do you like to eat?"

"I dunno, whatever me mum puts on table"

FACEPALM

I think it’s more of a thing with younger guys. It’s like something switches off in their brain. I’m sure there’s an actual term or description for it.

I didn’t really see many guys under 30 until I started touring, but I do recall one I saw who went a bit awkward and practically ran out of the room and out of the front door after he’d done!

It was sort of amusing really but I think if it had been civvy sex and before I’d done this job, I’d be slightly traumatised!!!