I don't know, but I've heard about a trick of taking the sleeve out and wrapping plastic wrap to the desired tightness around it, then putting it back in the case for a tighter feel. I think some people have used hair ties, too.

I think their production costs would go up a lot to have different tightness variations. Also it would make deciding which model to choose from that more difficult. I like the idea of the plastic wrap to the desired tightness. I have had other sleeves that were to tight to be used comfortably.