In reply to Ocala, another factor may be the arrival of HDTV, with the ability to run a couple of lower resolution channels off the same frequency assignment.
When it was analogue, you had one channel and that was it, and very expensive (not that the new equipment is cheap) to have that one channel on the air.
Now the big players have loaded two to six separate programs onto the same transmitter, and having the radar loop along with the last program presentation by their "chief" meteorologist is easy and a local crowd pleaser. So why would someone looking for the local forecast or the recent radar during violent weather on a nationally beamed channel which at best shows you a limited amount of info that rotates into view once every 5 - 15 minutes. And if there are hot spots, forget about that coming up.
Also, if they were running a 1/2 hour or hour program, forget about seeing some local stuff.