I'm completely on board with your RANT.
You ask why Google didn't enforce this in past years - because they didn't care. The Nexus phones weren't available (as far as I know) from any specific carrier - and even if they were, they weren't being advertised with any exclusivity like the new Pixel is with Verizon). This is why I think this action is not really coming from Google, but instead is Verizon putting pressure on Google to uphold their TOS so Verizon can squeeze more customers.
Google also most likely has a financial incentive here as well. I'm sure Verizon paid them millions for the exclusivity, so Google doesn't want to give it back, or be seen as a acting in bad faith for future business partners.