Recession of course - it gets everywhere. Pound shops and payday loan sharks don't compensate for the slide in mainstream business.
The 'win-win' relationship between web publishers and the ONE monolithic SE was ok for a while, but all good things come to an end. The one monolithic SE really isn't all that much different to, or better than the various SEs which went before. OK, there's been time to learn from experience and build on the software but the concept is quite similar to the old Altavista/Lycos days.
G has always failed to make a serious go of anything other than pure search. Now G+ is failing in the same way as other efforts which didn't work out. As an external observer, their tenacity with it is starting to look desperate: they know they need something else, but exactly what is far from clear.
In G's favour at the moment, my theory that the public is always 4 to 5 years behind the industry gives them 4 to 5 years breathing space.
My personal use of search has decreased significantly as the web has progressed - I know what's out there and the places I frequent online are bookmarked. SERPS which don't deliver the goods are the coffin's final nail. If I want to find something in the 'Walmarts' of the web (eg Ebay, Amazon) I'd rather use their own search because it gets me there faster. My mostly non-techy friends tend to have a similar take.
We need something new, different and, above all, good. Delivering it will be a tall order. If G can't I expect they will attempt to squeeze the lifeblood out of anything with any left, until there isn't any left at all, making those non-dividend-paying shares pretty undesirable.