> if a trademark holder doesn't engage in this sort of behavior, they could end up losing all rights to the trademark

[citation needed]

Other trademark owners aren't asshats like this about their marks and haven't lost them, have they?

Yes you need to enforce your trademark. But not against reviews of your very products, even if those reviews make their authors money through YT ads.

[Add.: and not in this way. I've read up a bit more, and they had a "valid" problem in that he used "LEGO" to refer to plastic brick systems in general. They do need to enforce that so the term doesn't become generic. But they could've just sent a message or letter first.]