Because if they try to fix it and change it to a sales tax, there's a panic.
A few years back (OK, like 16) they tried in MI. Raise the sales tax to something around 7% and eliminate property taxes for schools. That way EVERYBODY funds schools - tourists, business travelers, pimps, welfare queens, illegal aliens, etc... And - the level at which contributions are made is tied to income (i.e. consumption - the more you have, the more you spend, the more you save).
Senior citizens (who often curtail spending) get an automatic tax break.
People who save (instead of spending) aren't penalized.
However, like a flat rate federal income tax, it's too simple, too straightforward, eliminates the need for large state and federal tax staffing, and doesn't have any loopholes to allow people to bypass them, so it won't fly.
This is the Pub. Leave common sense at the door.