Here's why it matters, because I'm (probably) going to have to put in more time and effort if a sneaker only has 500 pairs produced than if there are 50,000 pairs. I would rather put in that effort before a release happens and/or just plan on spending however much money instead of striking out on release day because I didn't know about the relative supply and demand for a sneaker.
Case in point, what just happened with S Dubl and the red camos. People weren't sure if they would be limited, if they would have the full logo, etc. for awhile so S Dubl decided to just lock his pair up for above retail beforehand. Had he known that they would be widely available like they were I doubt he would've placed that order (and if I remember correctly he tried to cancel it once he found out the availability).
So that's why people ask.
Oh and also resellers.