My 2c:
* Companies, like the rest of the world, are now hyperconnected. We have slack and email and so on. This makes it a lot easier for similar interests to connect across a massive organization, which is a boon for special interest groups, like anime, or magic the gathering. Or politics.
* Companies muscle in on workers' identity. Workers respond to work over email/slack during their off hours. Workers pop open the laptop at home, even pre-covid. Companies try to justify this with a sense of pride, you should be PROUD to work for the great conglomerate XYZ. And guess what? If I'm proud to work for XYZ, as a worker I'm going to expect a consistent worldview that XYZ is aligned with my values. But my values are also tied up in my politics, so now I'm expecting my workplace's values to be consistent with my politics.
* The simple fact is that many companies are overwhelmingly a monoculture in terms of politics. It's easier to make your workplace political when 90% or 85% of employees are liberal anyways, as opposed to say 60%. This is largely a demographic thing, at many companies the target demographic for hiring is a strong overlap with certain political ideology (You are looking to hire a young, 25 year old computer scientist living in a big blue city who graduated from PresigiousUniversity. What politics do you think this person likely subscribes to?).