Big assumption that the average citizen’s opinion has any effect on what the government spends money on. It’s pretty easy to campaign on not doing X and then proceed to do X once you’ve won the election.
Consider that the majority of Americans do in-fact vote. In doing so, they literally delegate the power of the purse to the representative was most supported in their local community.
Look at the work put into ‘communication’ about those budgets also. In addition to having comptrollers to monitor the auditors or whatever.
The UK Expenses Scandal was funny, but Thatcherism is still doing too much residual harm to laugh about.
Promising x and doing y is a winner-takes-all democracy problem. Coalition governments solve this by sexing-up y as the natural outcome of the public vote. This also makes technocracy easier / more normalized.