IRS is a bloated lazy organization(like most if not all U.S. government agencies.)
They expect you to do all their work, then they have machines process it all.
Why do you think that?
The I.R.S. expects your employer to submit a form to them showing your income.
Any income that isn't reported they expect you to voluntarily list(like bitcoin gains.)
The I.R.S. expects you to compile that information into a single form for leisure IRS slackass reading.
What exactly do they do?
Sit around and eat donuts while reading all the information you compiled for them.