I cannot speak with IRS personal knowledge, but many who I have come across over the last few decades, will share generalities on actions which are done to protect self/department/office interests versus "real world" needs. In the "old days", many thought this was because some who even made it to decision power were biding time / building resume, towards personal practice. Complication/Byzantine means profits in PP, and life time employment whether in PP or not. An example is 94x electronic filing "ease".
Over complication and lack of accepting and using de facto standards is a real issue. IRS is not alone, see examples in CA such as their payroll process, EDD process, etc. Contracts for custom software which, after many years, is not completed/functional.
SSA, on the other hand, has easy efiling, and their MMREF file structure has been adopted (albeit sometimes oddly altered) by many other tax agencies.