"With platforms comes responsibility."
This seems plainly obvious to a lot of people, i.e. you.
But for me it's not obvious at all why. How do you justify that?
I've built a platform, much smaller. But it's still something I own and which I take great pride in. And if someone told me I had to allow it to be used for something that was abhorrent to me, well, I'd resist that.
That's the property rights argument.
I think people also miss that platforms are products in the case of social media and app stores. What I mean is that the content defines the product experience. This is different than say AWS or Google Cloud.
So, because the content defines the experience, these platform creators are always putting their thumb on the scale. Apple does it by encouraging specific developers. Twitter did it for awhile by bringing in live streamed NFL games. Etc.
Removing Trump from Twitter changes the product experience in a way that's good for some people and bad for others, and so it's just like making a feature change. There are tradeoffs. To me, it makes sense that platforms would consider curation to be part of the product experience.