[bamfly]

'07 was the height of Google's cat-and-mouse game with webspammers. It'd degrade to near-uselessness for a month or two, suddenly get a ton better, repeat. This went on though the whole of the middle years of the '00s.

'08 or '09 is when they seemed to surrender that fight, and just give up on indexing the entire Web. Major sites got a huge boost, and a great deal of the Web seemed to just drop off the index entirely. Google's never been really good since.

[tenebrisalietum]

Coincides with the iPhone, then the beginning of Android, and the rise of mobile overtaking desktop.

[bamfly]

Also IIRC right around the same time they totally abandoned "don't be evil" and started doing ads inline with search results, basing much of their future revenue on tricking unwary users.

[EDIT] They might also have switched from their text-only ads to being a more ordinary, crappy web advertiser not long after, which started to partially align their interests with webspammers, which may explain why they didn't mind yielding the whole middle (if that makes sense) of the search-result space to them.