In your example, the car company is implicitly selling to a foreign country. When it comes to software/websites, a user from a foreign country is incidentally served rather than implicitly.
That doesn’t seem reasonable to me.
Is "at least we tried"-style blocking good enough?
Yea exactly. In absence of a mechanism to block users the discussion of who gets to police who is worthwhile. But if a company chooses not to comply with GDPR and at the same time doesn't utilize any available mechanism to block EU users then there is definitely intentional ignorance on their part.
It's not the EU who wants to ban access to something. It's the provider who wants to benefit financially from selling that product( targeted ads) without having to comply to the laws of the country that the selling happens. There is no other market that you get to do that. Why should your web page be different?