> If so, then why does no other sport match its popularity in the US when NFL football isn't in season?

What does popularity have to do with artificialness? But, anyway, this is where it would be helpful for you to know a little bit about the history of the sport - the answer to your question is readily available with a bit of googling.

> If it's so goddamn arbitrary the something like baseball should make as much as it does.

Basketball is also an arbitrary and artificial sport. Many sports are. By definition.

> I grew up in The Netherlands watching (the other kind) of football,

That's good for you. But it is very obvious that the popularity of american foot ball is mostly due to societal influence. That is why it is popular in the US and almost nowhere else. The history of how and why it is so popular in the US is also readily available - if you're actually interested in that.

> Fuck you for assuming

Relax buddy, we're just having a civil discussion where we happen to disagree, no need to get emotional.