It’s more typical for people to “ghost”. I don’t think in those case there is any particular decision, they just stop checking in.

You’ll likely find the most common reason people leave is they’ve shared too much of themselves and someone either recognises them or they worry someone will. Some people start new user accounts and keep going. Some people will switch to a different instance. We aren’t a particularly attractive instance if you want to engage with a lot of lemmy.world communities, for instance. There’s a lag for when you’ll see their content until they upgrade their Lemmy version.