In fairness, I was working at a video retailer when this came out on DVD; dude, the first season just flat-out didn't sell. I believe we got a total of one reservation for it...yeah, that's not usually a good sign.
Reason being...the first season honestly wasn't that good. And since no one would buy a show's crappy first season, no seasons followed.
They could always replace the music with stock music; Malcom's not really a show where music seems like it would be so important, unlike say WKRP in Cincinnati, or The Wonder Years.