I was hesitant to post but here goes. I think there's a lot going on with this problem. For me it's a little of a lot of factors.
1- Time constraint. I usually book for 1 hour and that's the time in which I have to perform. I try to visualize stuff I want to do but it pretty much goes out the window once I meet the SP. I try to limit the chit chat at the start and get to groping and kissing. I can't really sog 2x in an hour anymore so after the sog, if I sog at all, I tend to talk and make the SP laugh.
2- Physical constraint. Getting older just sucks physically. I'm 43 and don't need pills, thankfully, but I know it's not been the same in the last 2 -3 years from before. Bad news, it's not going to get better either.
3- Condom. I've come to realize that for me, having penetration is so hard due to the condom. The smell, the slimy texture, it's just damn gross I can't stand them. So I stick to blowjobs, foreplay, dinner at Y, everything but penetration. The last SP it happened with was Jennifer at Euphoria, back in 2016. I was professionally in love with her, it just felt natural and wasn't forced at all.
4- Freedom. There's also a loss of freedom when dealing with the condom. I'd just like to have the freedom of, to be blunt, move from one hole to another freely. Obviously the influence comes from porn and from plain freedom itself. For me, I guess my brain computes that into the following formula, reality + porn = disappointed in life and loss of hardness. This thought pulsates in me throughout a session and even before, when I do try to visualize stuff. I'm going to say Hi, kiss her cheeks, offer her something to drink, chit chat, DFK, get a blowjob and not fuck because I have to put a hat on.
Those were my 4 cents. There might be more to it but I'm no psychologist.