I would say that it's because search engine ranking is good enough. At the very least we are in the domain of diminishing returns.
In terms of innovations, there was a weird and misguided attempt to integrate "social search" into your results, which thankfully seems to have disappeared.
There is also Google's Knowledge Graph, which is a promising idea but doesn't work well yet. Search for "calories in a cup of corn" and Google's answer is wildly off. Or try "activation fee" and find out that it's $40 (huh?). It remains to be seen whether this feature can be rendered trustworthy and relevant.
My Google results are noticeably worse for me logged-out (or through DDG) than logged-in.
This suggests that search is in fact such a hard problem that my search engine literally needs to know more about me than I know about myself to do a good job for me.
Which explains why Bing has such a hard time unseating Google - I'm always logged into GMail, so Google has known it's me doing my searches for the past eleven years.
In terms of innovations, there was a weird and misguided attempt to integrate "social search" into your results, which thankfully seems to have disappeared.
There is also Google's Knowledge Graph, which is a promising idea but doesn't work well yet. Search for "calories in a cup of corn" and Google's answer is wildly off. Or try "activation fee" and find out that it's $40 (huh?). It remains to be seen whether this feature can be rendered trustworthy and relevant.