I think its because you can get equal SPL out of a ported sub with less wattage than a sealed version. That means the amp and driver of a seal box need to be much beefier which is much more expensive than just designing a ported sub. And like everything in todays fast food drive through mentality world, cheaper sells more than quality.
All a guess on my part though, YMMV.
Edited by Jimna (11/13/10 09:56 PM)