"They are consistently bogglingly bad at human interaction -- communications, PR, management, UX, customer service."
I don't think that's actually true. In particular, I think that Google for most of its history was masterful at PR and communications - they managed to maintain a very positive public image all the way through 2011, despite being both far more powerful, more naughty, and more ruthless than the general public saw them as. I think management and UX are also quite strong at Google - they're known for sparse design and UX fails, but there's often a lot of subtlety to how Google products are designed that makes them very effective for their purposes. They did always suck at customer service, though.
Rather, I think Google's hubris is...hubris. They feel the need to have their fingers in everything. It's not enough to be the world's best Search company or even organize the world's information and make it universally accessible and useful, they also need to be the best social network, and best cloud provider, and best AI company, and best mobile-phone OS, and best web browser, and best daily deals site (remember their aborted Groupon purchase, soon followed by a competitor?), and do government contracts for the military, and get into China, and build self-driving cars and robotics, and be a major payment provider and operate half a dozen different chat services.
Most of the PR, communication, management, and UX fails are forced errors. They happen because there's an inherent contradiction in Google's business model. You can't simultaneously market yourself to engineers with "Don't be evil" while devising ways to help the military kill people more accurately or censoring Chinese search results; hell, at some point the military is likely going to have an issue with China potentially hacking into Google's cloud infrastructure through their partnerships. A surprising number of the UX fails also come about because some executive is protecting their turf and won't let the obvious integration & UI simplification happen even though both engineers and customers want it.