I propose an addendum (to the addendum, mine is the last line):

Those who can, do.
Those who can't, teach.
Those who can't teach, become critics.
Those with no criticism worth hearing, become "activists".

What happened to Silicon Valley?

It's simple. Silicon Valley, in the words of Zuckerberg, is an “extremely left-leaning place”. Except, it wasn't, as least compared with the rest of the SF Bay Area, as late as the '80s, when it was a moderately left-leaning place, with a libertarian streak, where plenty of conservatives could get jobs in high tech corporations. I know, I was one of them. BTW, a case has been made that a conservative workforce imported, together with their Protestant work ethic and self-reliant, problem-solving culture, from the Midwest, built the Silicon Valley, which would not, otherwise, be here. I was living and working, here in high-tech, watching all that change during the "dot com" boom, in the '90s". The first clear sign that something was off that I remember was that the invaders from the East were setting up shop in San Francisco. SF isn't Silicon Valley. SF is were Silicon Valley went on the weekend to take a break from hard work and long hours focusing on getting complex systems right, for a taste of depravity, and "it's cool". Setting up shop there was nuts, if the aim is to get technology right, because there is no culture for getting complex systems right there. But, they weren't looking for that, were they? They were looking to pump and dump, or, to have a lifestyle where they didn't have to do any work that wasn't "fun". I will suggest that the "extremely left" leaners from the East built comparatively nothing of Silicon Valley- they moved in here during the '90s, like a lot of Islamist hordes into Byzantium, without a Protestant work ethic or a culture of self-reliant problem solving, mistook SF culture for Silicon Valley culture, and conquest for competition, spread, like invading hordes, decapitating that part of the workforce which were "not a good fit with the corporate culture (now progressive) as they went, took the place over, and then claimed it all as their accomplishment. Of course they added a lot of elaborate (virtual) gingerbread false fronts on the technology, but, they are really a lot of sultans, ruling, badly, over the remnants of a culture they do not understand, which someone else produced.
I'm not saying there aren't real advances (like self-driving cars), I am saying they appear to lack something essential (although, that more or less every "idea" Elon Musk ever promoted I read about in an science fiction novel, short story, or maybe Popular Mechanics, 50 years ago might be, in this context, a comparatively good sign) to maintaining, and advancing, the heart of the thing.

Essentially, they are doing it wrong, like kids in Dad's workshop who do not understand the first principles, because they weren't willing to wait, or ask the old guy, or be corrected.

They did the internet (not really a Silicon Valley thing, BTW) wrong, I think, because the concepts were too influenced by progressive thinking in the universities. BTW, when Al Gore "took the initiative in creating the internet", he supplanted private networking companies, with architecture based on evidently different concepts.

I guess Silicon Valley was a kind of last outpost of somewhat strict laissez faire, at odds with a culture being molded into progressive conformity all around it. A beacon, which supplied technological progress, but also spoke, though not in words, but in the effectiveness of its culture, of something great, from the past, which our nation was wandering away from. Of course, progressive narrative-definers were the wanderers, so, they desired the product, without the principles, even unspoken. I don't believe that's possible- a leftist culture can't maintain a high technology civilization, or indeed any civilization, for long, and it certainly can't play fair enough to, er, co-exist with even somewhat strict laissez faire. At some point, the central purpose of leftism must suppress all other ideas, by any means necessary. So, Silicon Valley became an “extremely left-leaning place”.
Which may well mean that it's dead, Jim.