Purchasing Linux

I only discovered this because Louis Rossmann said in a video that he purchased Linux when he was a teenager and then showed the CD. I looked on eBay and I saw a few CDs that were still in their boxes and the labels that were on the box looked like they came from a bookstore, I did not know that these were sold commercially.

My question is, back when they used to sell these CDs in bookstores who was distributing the CDs and where was the money going to when someone made a purchase?

My second question is, if Linux is an open source operating system why would someone want to buy it? I still see some websites to this day selling Linux CDs, I'm really curious where the money is going when someone purchases the CDs.

Edit: I made a comment earlier but so many people replied I don't think a lot of people saw it so I will repost it here. "Thank you to everyone who replied, all of my questions have been answered, it was interesting reading through all the replies, there was a lot of different points that people brought up that I never considered before"

https://redd.it/1v5kxok
@r_linux