Because you're hired to get work done?

If you literally did nothing, you might get fired or at least your contract would not be renewed depending on who you are/where you are. Some people actually do that though, usually some nepobaby, and manage to avoid getting fired because they have some connection to higher ups.

I could probably get away with doing little to nothing for a good while because I've built up a lot of good will and favors at my job, but eventually I'd probably get canned. I'd also get pretty bored with that pretty quickly, I actually do like my job, I just don't usually go all out when I'm there.