My take is that the FTC is operating from a perspective that if you create content that's designed for children, and you put it on normal Youtube without labeling it, you're sort of "tempting" children to come into an unsafe environment.
In the Ars video, the FTC chairman says the following (16:30):
> "On the Internet though, you don't know who your users are. So what the COPPA rule more specifically does, is, 'where the content is directed to children, we are presuming the users are 12 and under.' [...] If however you are a general-audience platform like Youtube, you don't know what the content necessarily on your platform is. [...] That's what we mean when we talk about strict-liability for content creators."
To me, I interpret this quote (as well as the rest of the video) to say that the FTC does not care whether or not the platform is directed towards children. Keep in mind that Youtube is already officially designated as not directed towards children under 12. If your child is using Youtube, you are violating their TOS. My personal interpretation of this video is that the FTC is saying, "we don't care if the platform is for children, if the content is for children, the rules apply -- no matter where you put it."
As to whether or not content creators should be liable for Youtube collecting data that the creators don't even have access to, that's another question. But the FTC doesn't seem interested in asking that question. It's pretty clear to me that the chairman views creators purely as a means to getting at Youtube, regardless of what the consequences are to the individual uploaders. Creators are the "fish in a barrel."