You're unusual in that you actually noticed it and felt uncomfortable with it. As women, we deal with that stupid attitude all the time. The worst in my experience is restaurants, although car repairs / sales is a close second. So many times I've experienced the female wait staff fawn over my guy and barely acknowledge me. What they fail to understand though, is that much of the time it's me paying the bill, and hence, their tip ; ).

I think more men are into cars than women, I say this as a browser of automotive enthusiast sites and activities. Also, due to sexism and whatnot, men tend to (a) have more money and (b) want to blow it on cars. So, sure, they go to the guy. It's what works.

My understanding is that back when husbands were usually the primary bread winner, wives were the decision maker especially for major purchases. So maybe back then sales would be subtly directed toward women. Now that I'm a carpenter and my girlfriend is a fancy software developer, maybe things are different. If anyone knows who has more buying influence it's surely a car salesperson. They've got your number; it's their job. Maybe now sales are directed toward men so they will say "Oh, honey I think you should buy that one".

Does this make sense? Would any older women care to weigh in with your experience?

Conditioning. To quote Madonna "what it feels like for a girl".
If you think that going through life being treated like we are stupid is ok. Then yes, fuckery.
The boys and men who are raised to think and treat us like we are stupid. Yes more fuckery.
We women who really believe we are stupid because well, fuckery.
Do you see where I'm going here? It's a vicious circle. Thanks for noticing. But you should have gone a step further and confessed that you cussed out a car salesman for treating your girlfriend like she was stupid. Now that is the kind of fuckery we like.