> Unless the user is present and savvy enough to block it somehow, all of their short-term "throwaway" project/data just got deleted before they actually finished with it.

That's on them.

I use /tmp like this, because I'm lazy and don't want to have to mess with a directory I need to routinely clean up, but I know that if the computer crashes, it's gone. That's on me.

If you don't like this risk, you need to work in persistent storage.

/tmp is for programs' temporary files. Manually using it like this is abusing it. That's fine, it doesn't hurt anyone beside the user doing it, but they need to bear the consequences of doing it.