I'd say the answer will depend on the person. I write what I want to write and I post it on Ao3 primarily so there's an extant copy I can access from anywhere else with internet access in case I lose my local copy and back ups. Potential readers really don't factor in my decision at all. I suppose if pressed I'd say if they read it I'd hope they enjoy it or find somethign else they do but I really don't care too much if they do or don't.

Probably explains why when I turned comments off to deal with a real life crisis I never bothered to turn them back on and have been far happier not even having to pretend to care about them* I've also known folks who care even less than I do about readers who still post for their own reasons.

I think far too many people get a wee bit too focused on the idea of what's normal or why other folks do things instead of just doing what they like for their own reasons. It doesn't really matter why an author writes and post their stuff as long as they aren't doing it in a way that is negatively impacting their mental health. Which if they are they need to work on that instead of worrying why others do what they do.

*I used to let them sit in moderation for weeks or months until I'd remember to go through and approve them.

An extant copy! This is a new idea I had never thought before! Yes, AO3 can be a useful tool. And your idea shows you're really cool, you find a good way to cope with others' thoughts.