I agree, it should do. But many sites don't consider the “legitimate interest” crap (“we see your preference not to be stalked, but we want to anyway so you'll have to object separately”) to not be something that they have to get consent for, hence the option is to object/not rather than to consent/not. If you hit decline all without objecting to “legitimate interests” [sic], in at least some case, I suspect many, much tracking will still happen.

> The Google dialog kind of describes it perfectly: "Decline all cookies for this additional purposes".

IIRC Google's preferences don't include any legitimate interest gubbins at all, so that isn't really relevant. And just because one tracking nag screen does things a certain way, does not mean that many others work differently.