> I believe part of problem is Google SEO.
This and the fact that Google search is actually as dumb as a sackful of hammers.
Don't get me wrong, for the longest time Google's results were "good enough", but Google has no real concept of the quality of a result (they've tried and it worked for a while - e.g., PageRank). Still, fundamentally their algorithms aren't smart enough to figure out whether any given piece of content is intrinsically worthwhile.
That's really important in a world where most content is, regardless of Google's guidelines, primarily written for the benefit of GoogleBot, to harvest clicks or drive traffic.
Unfortunately Google has literally zero incentive to change this situation (because they're making an insane amount of money off the back of the status quo), so they won't[1].
Logically then, the time is ripe for a new search engine to disrupt but the problem - that of determining intrinsic worth - is really hard to solve, so as yet nobody has, and Google still reigns supreme as the most popular search engine.
[1] It is also possible that I'm being too harsh here: they might be trying to change it - perhaps because they're worried about eventually being disrupted - but, as noted in the following paragraph, the problem is REALLY hard.