They're so big that it's worth blackhats spending significant resources to game their algorithm. That induced them to implement a spam filter which is now discarding the ham along with the spam.
Which means that smaller search engines that aren't being targeted by spammers are now giving better results. That is a major long-term problem for Google if they can't avoid throwing the baby out with the bathwater like this.
People only use Google because it has historically had the best results. They'll get some way on inertia now, but that doesn't last forever. They need to fix this or they're ultimately in trouble, and we could be heading for a landscape where being a search engine above a threshold size is a liability.
It's odd to put forward the hypothesis that DuckDuckGo is now better at search (aggregation) than Google is at search. But that seems to be where we have landed.
I think Google has been explicit about this (I may be wrong, but I seem to remember thinking about this because Google themselves said it). Essentially, I believe, they are no longer concerned about being a way to navigate all the material found on the internet. Instead, they are concerned with answering the question posed by each search attempt.
A few years ago they made a push to answer questions to the point it was in their product description on their "how Google search works" page. To quote it exactly, it used to say their objective is to "return timely, high-quality, on-topic, answers to people's questions."
And that's kind of the whole problem and why there is space for a search that actually returns results from the web in a clear and logical way.
I've been thinking about this, and it seems very plausible to me. Which means that Google Search isn't really "search" anymore -- which explains why it's become so bad at that!
Too bad. I remember when Google had the best search engine going. It was a real game-changer. Those days are long gone.