In addition, I don't understand why they stopped them entirely, instead of spin them off as subsidiaries under e.g. Alphabet; make them financially self-reliant, have Google/Alphabet as the main shareholder, and give the people that worked on it (and whoever else wants to) the opportunity to continue working on the product.

Some wouldn't have been viable, sure. Others were probably too ingrained in Google's hardware/software ecosystem to be separated out (although I wonder if nowadays everything Google runs on its cloud offering, which would make it simpler, just change the billing).