this isn't a small change, it's a major platform decision that impacts user experience, usability and engagement -- it's also received strong criticism from the community including from the original founder of Youtube [1] (see description), but they're pushing it through anyway
You're being too naïve about the corporate agendas behind this change.
It's always been like they I think. Good people can't imagine just how evil people can be because it's so far from their own reality.
What is their political agenda?
Only if you consider egalitarianism and diversity as political issues. To most of society they are universal values so it’s not contentious.
It's not black and white.
For example, what do you mean by egalitarianism? Equality under the law? Well, Republicans/Liberals tend to agree with equality under the law, whereas Leftists and Gender/Racial Identitarians don't. California recently tried to repeal 1960s civil rights legislation preventing discrimination by race, precisely because they'd like to discriminate on the basis of race...because to them, egalitarianism doesn't mean equality under the law, but rather that the law should have weighted parameters necessary to transform societal outcomes into equal measures by arbitrary population, irrespective of those population inputs. Mind you, these are the people claiming to be egalitarian. As Ibram X. Kendi says himself, "The only remedy to past discrimination is present discrimination. The only remedy to present discrimination is future discrimination." To many (most?) people, that isn't egalitarianism...so it's political. It's clearly not a universal value when it's actually a bundle of competing values claiming the same word.
What about diversity? What, that diversity is just good? Is that the point? Because what exactly do you mean? What if there was a group of liberal people who had democratically made their society in accordance with what they felt aligned with liberalism, and were suddenly being told that a major influx of right wing evangelical Christians were to be allowed to come into their society (and be given exactly the same voting rights as them)? What about a group of frat bros? Is this the kind of diversity you mean? You just accept that diversity is indiscriminately a net positive? What exactly is the mechanisms that makes that be the case? Surely it matters what the cultures are that are being made to coexist, what degree to which they have common ground, what degree to which their respective strengths cover for their respective weaknesses, the rate at which the cultures can tolerate the encroachment of the other while still remaining cooperative rather than hostile, the degree to which each culture has its elements preserved independently of the product of the two cultures interacting, and the degree to which the cultures are encouraged to and are actively assimilating. I mean, this is just scratching the surface. There are many factors that determine whether or not diversity is actually a good thing, and it often comes down to magnitude and rates, which are seemingly unwelcome from that sort of conversation. And then there is the (now tired) distinction between superficial diversity and diversity of thought. There is the (racist) notion that diversity of skin color will result in diversity of thought, proposed by exactly the sort of people who actually detest diversity of thought, and just want to see different colored faces in the crowd. Again, this is just scratching the surface of this conversation.
So to say "it's not contentious" is pretty ridiculous, because these are completely loaded terms that mean completely different things to completely different people who ultimately have completely different goals for society. They're not universal values.
For one, Indian immigrants in the US disproportionately enter medicine, as do other Asians, in total constituting 17% of doctors. This is despite Asians constituting 6% of the population. 5% of doctors are black, despite constituting 13% of the population. In accordance with most advocating diversity for the sake of diversity, the reason for the disparity is assumed post hoc to have been due to discrimination...but why? It's as if the inputs have absolutely no bearing whatsoever on the outcomes. In order to seek population parity, that would mean arbitrarily capping the number of Asian doctors, and arbitrarily pulling black doctors from a pool of applicants that literally doesn't exist.
Rather than a deontological approach, of perhaps simply ensuring that the hiring process is as blind and devoid of bias as possible, diversity advocates are instead interested in diversity for the sake of diversity.
Again, this is political beyond just "being a good person" or not.
But I don't think there is deep evil thinking behind dislike change - in large corporations people need promotions, some entrepreneurial PM and couple devs identified the opportunity and went for it. Directors/VPs are too disengaged to truly understand impact of changes.