Even when YouTube has videos uploaded by doctors having to put up with this kind of stupidity, it doesn't change the fact that hardly anyone does that. The vast majority of stuff uploaded to YouTube isn't even that. It's losers trying to get views.
The reason is legal liability, generally.
If you sell Q-Tips and tell people to be careful when sticking them in their ears you're likely to be held legally liable when someone isn't careful because there will be infinite wiggle room for them to claim you didn't specify the safe use clearly enough.
If you sell Q-Tips and tell people not to put them in their ear (even though you know that's why most people are buying them) then when someone sues you for messing up their ear you can tap the words on the box and say "well, we told you not to do that".