Generally speaking the average person who buys an EV is better off than the average person who buys a gasoline/diesel car, new or used, the reason being that EVs are on average more expensive compared to the same class of vehicles which are powered by gasoline/diesel (to say nothing of the fact that I don't know of used EVs that can be purchased under 4,000-5,000 euros, of which the roads around me are full of).
As such it makes sense to tax more the people that have more money, you aren't going to get as much money from a single-mum driving her 1.2l Opel Corsa compared to what you can get from a programmer/lawyer/real estate investor who drives a 80,000 euro Tesla.