If government coffers are a barrel with a bunch of holes in it, and taxes are water pouring into the barrel, why are we constantly fixated on increasing the rate of water entering the barrel, and not on plugging the holes water is spilling onto the ground on? The government is notoriously wasteful with tax money, so why are we unable to incentivize more efficient usage of existing taxes vs. increasing tax income?

It's like a software developer who always adds more and more RAM to their PCs and always frames the problem in terms of how much more RAM they need to make things work instead of taking some time to close a couple thousand chrome tabs.