Giving low scores is, as called out in the twitter thread, stack and ranking managerial BS which is toxic to its employees. Low and high performing employees.
If you don't have strong incentives to fire low performers (aka stack ranking), end up with a slowly deteriorating engineering culture as more capable people end up carrying the weight of worse hires that don't get managed out. Those devs enjoy their jobs less and leave for better pastures (because they're options are good), while worse devs stick around longer (because their options aren't as good).
If you do have strong incentives to fire people, you end up breaking up high performance teams, and create a culture of hire-to-fire and "mercenary" devs. This impacts your culture and forces out "good enough" employees and causes higher recruiting costs.
I don't fully understand if either of those are right in this situation, but I understand how people who felt they were with one type of company can be upset if that company changes its "culture" without a lot of heads up.
You could presumably still give low ratings before when it was merited.