> So just make a rate card for data centers that ensures the burden doesn't fall on residents.

This is actually what happens in most places. It's even what happens in many cases when the data centers are given a discount, because the "amortize fixed costs over more units of generation" thing still happens.

Higher rates are essentially a time lag. You want to add load to the grid today but it will take five years to add that much new generation and in the meantime the only way to make a higher demand curve match up with the existing supply curve is at a temporarily higher price.

You could raise the price of electricity on only the data center by so much that it removes the increase in demand, but what that actually means is not building it there, and then it also isn't there after generation catches up and the local power company would have been able to spread their fixed costs over more units.

> I've also seen counties offer tax incentives. Why? Just have them pay property tax.

Data centers are asset dense. A large one would have a value of e.g. a billion dollars while the neighboring plot of land has an assessment value of a million dollars. That's why they offer tax incentives -- a tenth of the rate on 1000 times the assessment value is a huge revenue win over the 100% of nothing you get if they build it somewhere else.

Or to put it another way, it allows the towns with a higher mill rate to keep themselves in the running instead of being excluded from the outset.