Question about Teespring Traffic

Hi,

So I looked at analytics for teespring.com on Similarweb.

https://www.similarweb.com/website/teespring.com#social

And I was really surprised because Youtube is the largest source of traffic, way larger than Facebook.

As far as I know, most of people doing Print on Demand use Facebook Ads as their main advertising method. And many say facebook ads is the best for POD. So I'm really confused. How teespring got so so much traffic from youtube??