I'll throw this reason out there:

The networks don't know that there is that much low end content in their mix so they don't do anything to roll it off. Most network audio control rooms that I've been in, e.g. MSNBC and ESPN, don't have any subwoofers. Thus, their audio engineers don't necessarily know just how much bass their mixes have. Most smart ones, however, will roll off most bass below about 100hz for almost every vocal microphone to avoid picking up an rumble from movements on the set.

Don't read me wrong here. The audio engineers, for the most part, know what's going on with their mix. The issue is more with master control and the suits who design the control rooms.

Just my .02 cents...