Electric cars still need maintenance. They don't get regular oil changes, but they wear out tires sooner. They have more recalls in general than ICE (this will likely change, but manufactures are still learning how to make EVs reliable). The parts of a car that are not common with EVs don't break for the first 100k miles, and almost nobody is using the dealer for cars that old. There is plenty of other work that is common that dealers will still need to do.

Your argument hinges on any level of maintenance being enough to maintain our current level of investment. The truth is always more complicated.

Take for example DVD rental. The market completely evaporated, while there is still a small lingering community that could be serviced by rentals. My local library is proof that there is a market. But there are, bar some weird exceptions, no remaining DVD rental stores.

If an EV needs 50% of the maintenance, then it stands to reason that you need 50% of the staff. That's the easy part. But what about all the other staff? Can you afford as many staff in front of house when your main profit centre shrank massively? Can you keep the same amount of cars in the lot if you don't have the cash to pay the manufacturer fees?