When you are mostly just shown content that you’ve agreed to see, there’s less of an issue when you see something that offends your particular sensibilities, values, etc. because you agreed to see it, or you went looking for it.
But when the potential content you’ll see can include literally anything, there is a real incentive for the platform to make that content as neutral as possible. Because if you’re shown something that you really don’t like, you’ll stop scrolling and the engagement stats will go down.