I think yorks and Fred sum it up, OP.
I think what you're neglecting is that we're all different and enjoy different things. Age is a major factor as well. I doubt some senior punters on here would value a splash and dash 30min punt. Similarly, younger guys may just want to get in, bang a bird and be off. A lot of us like to take our time and enjoy a bit of good, old-fashioned foreplay before the main event.
Myself, I'm a one pop merchant and used to do hour punts. I've recently reduced these to 45mins , as I lose very little, but can save a few quid. Half hours can be a bit rushed and use these on toftt punts, or if their hourly rate is high.
As JRC says, price differential comes into it. I saw a girl a few weeks ago who charged £70/£140. When I asked the 45min price, she quoted £120. Half an hour it was. I prepared for a quick job which went ok, had she quoted something more reasonable I'd have done 45mins. She lost out.
Then there's frequency if punting, the thrill of the punt, which is what does it for some. Short cheap punts satisfy that urge.
At the end of the day, if someone wants to pay a girl £200 to talk for an hour, its their choice. Satisfying your own needs is the most important thing!
tcm