Because decades ago the collective we decided that everyone should pay for the residential grid because everyone benefits - much like a road. In some states you can't disconnect from the grid even if you wanted to.
So now some small percentage of people - 1.4% of cars are EV - are adding loads to the existing grid to the point where its almost at peak. Different areas vary, but the older and more densely populated the area, the generally worse it is.
So the grid needs to be improved. So they want everyone to now pay for the 1.4% or whatever percentage of EV's will exist in the future. Thats not exactly equitable, that the 98.6% subsidize the 1.4%.