Social Security systems contain tens of millions of lines of code written in COBOL, an archaic programming language. Safely rewriting that code would take years—DOGE wants it done in months.
Probably a mix of Z systems, that stuff goes back 20-odd years, and even then older code can still run on new Z systems which is something IBM brags about.
Mainframes aren't old they're just niche technology, and that includes enterprise Java software.
Chatty government contractors. I imagine some parts are updated but at least 2 years ago there was still a load of legacy hardware kicking for them to speak of