One moment? Have you created a Google account recently? It's not nearly as easy as it used to be. Wants to know DOB, gender, a working phone number that they verify, etc. Seems to me that by linking the phone number to what is probably the same phone number for your other Google accounts, you may as well just have used your main Google account to begin with.

Google will know (and can even be pretty sure based on correlation of other things, like endpoint location if you tend to use multiple accounts from the same IP address) but at least the car dealer/manufacturer won't have your other email address, which solves for one possible threat model.

Are any of those hard requirements? I figure a phone number is at this point, but DOB or gender?

KYC policies, probably. Though asking for gender sounds like an unnecessary mine field.

There's that, but even DOB feels weird. And about twice a month when I log in Google tries to get me to fork over my home address.

KYC outside of industries like banking frustrates me to no end because when it comes to things like money laundering, they still drop the K. I'm reminded of an anecdote from a book I read a while ago, that some rich European had a really big account with either Chase or JP Morgan and his name wasn't attached to that account in any of their internal systems because he requested it.

The same way we have catch-all email addresses, we need catch-all phone number redirects.

It has to be the first one or these companies will never change.

Car dealerships are an insulating layer to protect manufacturers from the repercussions of the bullshit they inflict on customers. In exchange, dealerships are allowed to inject their own layer of bullshit.