Only the mega-cap ones started to pursue other options mostly due to their type of business and bucket-loads of "free" VC money with explicit orders to burn it and get "unicorn" status - which involves hiring thousands of developers in record time and the whole thing turns into a zoo. Which is an organizational problem, mostly not a tech one.
Other than the ones we pretend are the whole Universe, there are thousands and thousands of medium to big companies with billions of revenue who started their product with a monolith and a MySQL database and many still do just that.
My main point is attempting to counter the narrative popular on HN that postgres should be an automatic default. For sure there are many aspects in which postgres is superior, I absolutely do not debate that, especially when it comes to developer experience. But there is much more to it than that when it comes to delivering business value. That's where ops and DBA concerns start to matter, and IMO MySQL is so far ahead in this regard that it outweighs all the other hideous warts of working with it, when you consider the bigger picture of the business as a whole.