I agree wholeheartedly with the sentiment, but as an outsider, it's hard to judge exactly why Google (and other major offenders like Facebook and Apple) have lost the plot in recent years.
I suspect a big part of it is believing your own hype. You have a goose that has been laying golden eggs for more than a decade, as a result of which you have an army of staff paid astronomical salaries and effectively unlimited budgets to do anything else, as long as the goose is protected. This removes any need for efficiency, effective feedback loops or any kind of meaningful customer support or service standards.
And notice that the goose is always protected. Google's search UI is still very similar to the money printing machine that launched it all those years ago. Facebook's whole UI is still built around a news feed and the concept of keeping up with people you know. Apple still operates a mostly closed ecosystem with expensive but relatively good and prestigious devices and strong control over the software ecosystem that has grown around them. No-one is going to risk undermining the foundations any time soon. And the rest, frankly, doesn't matter.
This wouldn't be such a problem except that the immense financial power and network effects that these huge tech firms can bring to bear are enough to move national economies or to create or destroy whole industries, industries that might be supporting millions of users and providing livelihoods for millions of people (or, tomorrow, might not). While the success or failure of a new moonshot project might not be here or there to the senior executives preparing for their next quarterly call, it might accidentally crush a startup that much better people had spent many years working on and done a much better job but without the unlimited budget and free publicity. While shutting down the latest adventure into social networking might be a footnote on the annual report, it might inconvenience millions of people who had invested their time into getting set up on it. While breaking email as we have known it for decades in the name of fighting spam (badly, of course) might be a little "oops" for Google, it's screwing up communications between friends and between work colleagues and between businesses and their customers all over the world.
These tech giants are a plague on society, managing to limit or even reverse progress across the whole tech industry and undermining the efforts of millions of people to make the world a better place with all the amazing things we know how to do today. It really is long past time they were broken up, and all the other things they do forced to stand or fall on merit instead of leeching off the goose's golden eggs. The broken UIs are just one small symptom of a much more fundamental problem.