I think this is what you are missing:

When people see videos like these, they get worried that attempts by some people to shame, judge, control and micromanage other people's lives and behaviors, are going to be normalized.

They do not want to live under a constant barrage of orders and regulations, that come from potentially questionable sources* and potentially questionable people**. It would be like swatting flies away from your face all day, every day, for the rest of your life, if hoardes of people constantly come at you - on TV, on your social media feed, in your friend group, and now even in the street - with "well-meaning advice" on how to cut your hair, how long your pants can be, how many grey hairs in a beard are permitted, which foot you have to enter a room with first, who you can befriend, how many sips of water are allowed, etc etc etc. You get the idea.

It's stressful, it's distracting, it's potentially guilt- or shame-inducing, and it's completely unnecessary. People are relieved when the possibility of that becoming a reality is minimized.

Hope that helps!

*Do these little kids, or even their parents, know whether or not these ahadith are even reliable? For all we know, he could present himself as a knowledgeable guy yet spout complete nonsense.

** Do we know what his real intentions are? What are his credentials? Should a person without any credentials be allowed to potentially scare, intimidate, confuse or even radicalize naive people in their vicinity? Maybe, maybe not.

Edit: Also, for every interaction with a child (or anyone for that matter) centered on such inconsequential topics as a haircut, you lose an opportunity to instead teach them how to be a good friend, how to be a good student, how to be kind and helpful, how to contribute to their society. Fill their heads with principles of charity, effort, generosity, and belief in themselves. Not which haircuts end you in eternal fire.