But the onus is still on the developer to choose _what_ gets a unique URL and what does not.

It might be good for user deeplinking capabilities to change the URL every time any type of state change is made (for example sorting a list by date instead of name) - But exposing that many URLs to Google would be bad.

(This is the modern equivalent of the age-old "infinite calendar" problem that Googlebot had to deal with when dynamic calendar apps let you navigate to dates 2 millennia in the future.)