I've certainly had encounters that were strictly "show up, get fucked, leave", but they tended to be one time events, not repeaters. There were exceptions, though...
An interesting one was a young woman who met me for drinks in the hotel lobby, and we had agreed ahead of time that it was BCD from the outset. It was winter and she had on a long coat that she never took off. We got up to the room and she took it off, to reveal nothing but lingerie underneath. I remarked on this(!) and she said "It saves time".
I saw another college girl, a sorority girl who was using SA for college expenses and her sorority dues. She wouldn't stay long, although she was friendly, but we would get right down to business and she was gone within minutes after the sex was over.
But, the best one....started out that way. A local model, heavily tattooed and utterly gorgeous, who was business-like but great in bed, if a bit reserved (at first). She would come up to my hotel room and we would have a great time, and she would leave. BUT...since I turned out to be "not an asshole" this evolved into a real friendship, and I saw her regularly for almost a year and it gradually changed into lunches, dinners, and a lot of hanging out, as well as just explosively good sex.
So, you're right. The get laid and get paid women are certainly there on SA, and the price (where I live) is about 1/3 what escorts charge. The downside is that you have to live with a MUCH higher level of last minute cancellations. But, it's kind of spoiled me and going back to escorts would be difficult, and much more expensive.