Not an industry insider, but just posting as a (n obsessed hockey) fan, here's some theories from me as to why we don't hear hockey talk:
1) ESPN has rights to the NBA, not the NHL. Whether by choice or not, ESPN prefers not to discuss hockey.
2) Fox Sports Radio is based in LA, not a hockey savvy area.
3) Yahoo Sports Radio, apart from Szabin in the morning, has little hockey to offer.
Here in Pennsylvania, I truly think the NHL is covered and talked about more thoroughly than the NBA. The state is covered well by pro teams in the NHL, AHL, ECHL and even a team in Junior hockey In Erie. The NBA has the 76ers and even in their home city, they ranked 4th out of 4 of the Big 4 pro sports.
Most of the radio talkers, gleefully profess their ignorance of the sport. Several of the more well known ones like Colin Cowherd, Doug Gottlieb and Dan Patrick, profess their love of the NBA. For the most part here in PA, the NBA doesn't even register. The NHL - on the other hand - is all over the map, especially now with the Penguins-Flyers playoff battle.
Seems like the only national talker who will discuss NHL hockey is Jim Rome.
So to get my hockey fix, the TV is always on NHL Network. And to heck with the radio!