In states like CA, this means paying $4,000 to $10,000 in sales/use tax with each purchase. It’s an incredibly inefficient way to pay for having access to a car. If you’re going to trade in that frequently, it’s probably smarter to lease. (I say this as someone who generally opposes leasing and has never done so.)
It does cost money, but if you sell, you can pass part of that tax on to the buyer, as they’ll want to pay a bit more to avoid having to pay that tax themselves.
I don't think that's possible for the vast majority of people. A car should reliably take me for A to B and not lose 70% of its features just because the manufacturer decided to EOL the online service.