Yes, young escorts are getting rarer, especially British ones. This is a well established trend that's been underway for decades.
But no matter how logical is seems to some, OnlyFans is not a major reason. It's a well established result from studies that only a tiny minority of lasses make good money on OnlyFans. Most have to graft to make even £150 a week. Which also matches what I've heard from young women direct. E.g. Brooklyn (my second review) who went on OnlyFans after lockdown. Back then she was only 23, good looking British lass with a fantastic body, but other than matey boy myself, hardly anyone was giving her anything.
As other have suggested, better prospects in the Civvy job market is one reason, at least if we're comparing all the way back to the 90s when more young women went into sex work out of economic desperation, even ones not cut out for it. For decades now, lasses have been getting better grades than lads in education, and in some years those aged 20-30 even earned more than their male peers.
But by far the biggest reason for the tend is decades of falling birth rates. This causes an inverse population period that especially hits the number of young women available to become escorts. (And to become Sugar babies & civvy girlfriends for that matter) If any are interested, I explained more here:
https://www.ukpunting.com/index.php?topic=402685.msg4069635#msg4069635
