In a sense they all compete with each other. They are all designed as an addictive feed of shit to click on while they insert ads in between. The fact that the demographics are a bit different just shows that competition is working as they want to divide the market, it’s not typical that competitors exactly get the same demographics. For example, consider who shops at IKEA vs Pottery Barn.

It didn't just say demographics so I think that's a bit reductive. That's just like saying "all retailers sell you crap" so Ikea, Footlocker, and Barns and Noble are competitors to each other.