If that’s the case, then why does every dental plan cover routine stuff and barely help with emergency?

Dental “insurance” is exactly the opposite of what you said it should be. It covers routine stuff but lol if you want to use it for anything else, what with their max coverage for a plan year thing and all (which routinely is far less than half of your out of pocket cost for anything other than simple fillings, and if you weren’t paying for the do-nothing insurance every year, you’d be in largely the same financial position)