I've paid for sex three times.
Once I was new to the West Coast and with no friends and I made eye contact with a pretty junkie walking down my street. We started talking and she asked me for money, so I proposed a trade. She was up for it so we walked to the atm and in the street she let me feel her breasts for a few minutes. It was a letdown, but I felt slightly thrilled. She was hot but sort of gross.
Several years later, I came home from a family visit late one night and was feeling energetic so I went to rent some pornos. As I was leaving the store I picked up a free magazine of ads for escorts, and when I got home I called one. She told me it would cost $300 on the phone and I agreed. When she got to my apartment she took the money down to her companion waiting in the car. Then she came back and wouldn't have sex with me! I was pissed. She was conning me. She finally did a strip tease while I masturbated, then left. I felt totally pissed and sad/ashamed hateful of myself and her. I basically resolved never to deal with prostitutes again because that was so shitty. It also made me somewhat misogynistic in a way.
A few years later I was driving on a rural highway and saw a sexy hitchhiker. I had this weird feeling so I turned around and picked her up. We drove for a while and talked, she was cool. When we got to my turnoff she said she needed to go another twenty miles and she would give me money if I would drive her the rest of the way. Instead I suggested that she give me a hand job instead and I would drive her. She said ok but only a handjob which was fine with me. That was a fairly pleasant experience overall even though it seemed kind of scandalous to me at the time.
The first and third weren't really formal prostitutes, but it was prostitution right, so I include them.
As for why, I'm kind of a oddball guy, I don't go to bars, and I am introverted, somewhat shy. My family of origin was dysfunctional and abusive, and touching and intimacy were never something I saw nice examples of until basically my twenties. I have had a number of serious girlfriends, but I tend to go a few years between them with practically zero hookups in between. Like most guys, I get very horny, and want someone to hold and touch. I don't feel like it's a desperate desire to avoid loneliness. It mostly feels like out of boredom and desire for physical stimulation and release.
I don't feel any regret or guilt consciously about these acts, though I wouldn't want people to know either.
It is sort of sad, but I do think paying/trading for sex has been around forever and serves a function.
I think it would be better if it was legal and not as marginalized where abuse and violence enter into it.
I don't think humans have figured out a functional form of sexual relationships. Traditional gender roles seem useless and non-productive, and these are generally mirrored in sexual roles and representation. Of course, that is true in prostitution as well, but to me it seems fairly rational and straightforward, which is more respectful of the participants than the unconscious charade psychodrama that usually constitutes regular romantic sex.