Because the fee revenue was created by congress, so the money goes 1/3 to Treasury to help pay national debt (doesn't really make a dent), about $1.6B goes to the government general fund. But FY24 collected $4.5B in fees, but the budget was almost $9.5B.

So even if all the money went to TSA, less than half their budget is covered. There is inherently bloat in that, but that is for a different discussion.

But bigger still, if Congress didn't reappropriate that money from TSA, they'd either have to spend less (less likely), raise taxes (not likely), or go deeper in debt (very likely) in order to cover whatever they are currently covering with their 70% share of the fee.