> They do it because advertisers are threatening to pull their ads off the service entirely if there's a risk of being placed against offensive content.
But who decides what is offensive? Are videos about gun safety "offensive"? Until recently the answer for that would have been "no", but not so any more.
The terms for what is considered "acceptable" is getting smaller and smaller all the time, people get less exposure to things which challenges their views, making them even more likely to be "offended" by even more harmless stuff, even facts.
If you look for right-wing channels, anti-religious channels (which includes criticism of Islam!) or worse, anti-feminist channels (you know, people who would rather have equality over specially honed women's-rights) which has been demonetized by YouTube, you will find they have been hit across the board.
If you however look for left-wing, pro-immigrant or feminist channels... I challenge you to find a single one which has been banned or demonetized for being "offensive". These views are for some reason not affected by this increasingly narrow definition of what is "acceptable", despite many of them being openly sexist and racist.
With certain platforms completely dominating the market (like Facebook & YouTube), having non-leftists either banned or treated as second-class citizens can be considered quite undemocratic.
People who previously could engage in a reasonable debate in a diverse environment (as in diversity of thought, not some token superficial "diversity" in forms of race or sex) are now being excluded, pushed out, into what certainly will be non-diverse echo-chambers.
What the long-term effects of such actions are can be hard to predict, but I doubt they will be good.