That’s probably a very old system and it actually works pretty well. My guess is it’s some ancient mainframe or even pre-mainframe app that is running on batch

That’s probably a very old system and it actually works pretty well. My guess is it’s some ancient mainframe or even pre-mainframe app that is running on batch jobs that still require production control overseen by humans. Federal budgets aren’t like private sector. They don’t just allocate $2B for the IRS commissioner to use as best suits the business… specific programs and tasks are authorized by congress. In the case of IRS, there’s a group of people in congress who are dedicated to IRS performing as inefficiently and ineffectively as possible. (For some things, earned income credit enforcement is fully modernized and effective)