Your happy hooker pep talk is nice but irrelevant, because if it weren’t for guys with hangups about women and their own sexuality sex workers would be out of business. No one goes into it as a first choice, client or provider. For me that’s not hard to accept, because where else is a guy my age going to get sucked and fucked by a bunch of different girls around 19 or 20 (and I don’t care about keeping my ATFs around for long because youth is market value, there will always be new younger girls providing the same services). I’m not going to be an asshole to a girl but she’s there to provide a service like you said, and I’m focused on getting that service.
I don't think the industry needs people with damage or hangups to exist, to be honest. I think if sex work was more accepted and not shamed or illegal, demand would be way up. It would be like any other indulgence, like spirits, cocktails, food, massage, live entertainment. It is that already, it's just shrouded by this cloud of destructive puritanism and shame that those other luxuries don't have. If anything, sex work has the ability to lessen inhibitions and expand boundaries for clients. It's often effectively therapy, or a safe space for exploration for a lot of people.
Lots of providers don't enter the industry as their first choice, but some do. I think what matters most is why they stay; if it becomes their first choice somewhere along the line, it is their first choice.
As for clients, sex work is often a first choice because it comes with no emotional responsibility. Plus sex with civilians is hit-or-miss, and costs far more in time than it does in money. Aside from that level of access and quality, there's just an inherent difference between sex with someone you're attached to, and sex as a conversation. I enjoy both, and I doubt I'm alone in that.
To your other question, I think people quit and return and quit and return for different reasons. I'm sure for some, it's because they find work outside of the industry less fulfilling or specialized in ways they're no longer fit for, as you mentioned. Realistically, doing a job anywhere for a few years can leave you feeling behind the curve in other career paths. Others return because they genuinely like it. Making their own schedules, working with likeminded providers and clients, living what's essentially the contract life instead of the salaried life. I'm a contractor myself, so I get it. A rare few also just thrive on the job itself; experiencing other people's sexuality, and exploring themselves as well. I think that's a more popular line than it is a truth, because it's a flashy thing to say, but I know for some it's a very real attraction.
I don't think we can really generalize about why people leave one career and then come back. I'm sure for some you're right, failure is a factor. That's present in any industry, and it's sort of the impact of living in such a specialized age. But for many, there are lots of other reasons. It varies from person to person, I guess because sex workers are people like everybody else.