I swear that our refy on our mortgage took a lot of extra paper shuffling because of those occasional little cash deposits...
we live in scary times...
The mortgage paperwork is absurd. It’s so complicated and long that no one ever reads or understands it. It’s the bureaucratic blindspot - bureaucrats believe that they can make things perfect with more and more regulations and thus, more and more paperwork. Simpler contracts work much better.
The IRS knows this, and stays complex on purpose.