That happens because Congress wants it to happen. They have cut funding for high value enforcement and pushed going after low income filers, which is both amenable to their major donors and helps fuel the narratives about big government and taxes being too high.

This also plays out in other ways: Intuit spreads a ton of money around trying to prevent the kind of automatic tax and online filing which happens in most of the world because thinking of taxes as hard provides them with a steady stream of customers.