They are complementing the federal government so it doesn't have to provide these services.
If federal government would take care of everything and this was some extra service then I would agree with you, but it isn't.
And citizens in high tax states with high benefits that only benefit the local population get to reduce their federal tax burden with SALT deductions that others in the country don't benefit from.
Apparently I have to get more hypothetical, imagine 49 states introduce a 100% income tax but with that tax revenue, they give free rent, free food, free healthcare, free netflix, the works. With unlimited SALT deductions all of their income would go to the state governments and the 1 last state would be covering basically the entire federal budget (they get some from other things like corporate taxes).
Obviously totally unrealistic but the point is that increases in state and local taxes with SALT deductions benefit the state and local population at the expense of the federal governments tax revenue.
You overestimate how difficult this would be for the vast majority of people.
> imagine 49 states introduce a 100% income tax...
So your solution is to ask the citizens of states with 100% tax rates to pay > 100% of their income in taxes? How would this work?