It is unusual. Google uses some of those cookies to determine whether it can lower the "threat signal" on your user agent (a UA carrying tokens that only Google could have issued to it is a huge indicator that Google has a pre-existing trust relationship with that UA).
By throwing away those cookies, your browser is doing the equivalent of showing up to the Google DMV wearing a different hat / sunglasses / beard pattern every time; the agent behind the counter can't say "Oh, that's just tomxor, I know them at a glance already so I by default trust they aren't an active threat to me" and has to do the equivalent of going through the process of doing a background check on you every time.
> But Google is optimising for the 99% at the risk of locking out 1%, that seems careless to me.
It's not careless; it's extremely intentional. Google has a responsibility to protect the 99% and assumes that those who are Internet-savvy enough to do the work to wonk up their UA's thumbprinting are Internet-savvy enough to do the additional work to make that process smooth for their fancy non-defaults configuration.
At the scale they operate, you can expect Google to make the decision that benefits the 99% over the 1% most of the time (particularly when it comes to account security). They'll assuredly risk losing business by making the 1%'s auth story more inconvenient if it makes it 1% more likely that the 99% don't lose the whole farm to a hacker.
