I did retirement home training and used to think it was a sweet job. Then I got in the business and underestimated how demoralizing it was as they give you the easy elders in training while the others make you, or at least me, really think of the fact the job just amounts to an unkarmic freebie.
I would say many of them are there for a free paycheck yes, but personal trainers are also there to teach people who have never learned how to exercise how to exercise and to encourage them when their friends and family will not, and those are valuable if time limited resources.
It’s also motivation. Sometimes I ask for a few sessions as a birthday present because it’s the only reason I’ll actually go to the gym. Accountability.