Every single one of us has been bitten by auto save that didn’t work. I’ve personally lost hours worth of code to auto save glitches and poorly timed save runs. People don’t trust it because in the past it has had and/or caused problems with their workflow.
Ctrl+S is a manual confirmation that I saved it, and is a step taken before running any code, especially through a terminal in an IDE where if the auto save hasn’t kicked in will mean the changes aren’t reflected.