As a Seattleite, I don't think it's fair to blame Republicans in this case: my city, county, and state are dominated by Democrats who promote Vision Zero[1] yet refuse to do anything about these obscenely large (and growing) vehicles.
It's safe to say that no Republican is going to win city/county/state-wide office around here, so the "attacks" are moot. For example, the state's hurtling towards passing an emergency AWB into law, all while Republicans yell and scream. So, again, the Republicans ain't the problem.
Are there any policies that Democrats could enact that would make them lose support? The answer is clearly yes. Is taxing vehicles enough to pay the true cost of road maintenance such an issue? I don’t know but it may be one that Democrats don’t want to tangle with. Such taxes are done at the state and national level and I think this is an issue they don’t want to give Republicans a win on.
Edit: The nation as a whole has shifted very much rightward the last 50 years. Instead of saying Republicans I should maybe say “right leaning politics”.
Office-chair-stealing Tim Eyman and his supporters would likely get an initiative passed that disallows any limits or weight-based fees. It's not a winning strategy, unfortunately.
Michigan is the home of the US auto industry and that state is filled with politicians from the Democratic party. Ford and GM are making some mighty big vehicles and I'm sure their elected representatives (Democrats) are doing their best to encourage it.
Where's the disconnect? The OP claimed it was purely a republican move. The reality is that the powerful people in Michigan are Democrats and the state's top tier companies make some of the heaviest cars on the market. If the Democrats wanted to do something about it, they could make the cars illegal and also put some of their citizens out of work.
But the reality is here in the States it's not the EVs that are the weight problems - it's the mega trucks and mega SUVs. The vehicles people drive today are comically large compared to those we were driving when I was a kid.
1. Not give an opponent an easy way to attack you that requires the masses to employ nuanced reasoning to understand why that attack is wrong.
2. Say things to your base to keep them voting for you even though you have no intention of implementing those policies.