The Eagles, and NFL in general, are too valuable to be thrown on a smaller signalled AM, talk, music or otherwise. Phillies are great to listen to on WMID and WCMC...music stations...but there's 162 games, plus preseason! Sixers and Flyers also play many games, are not as exciting on radio, and have proven themselves mediocre in listenership.
Eagles play only 20 games, including preseason. It has nothing to do with being on a music station, it has to do with the target audience, specifically men. It's a great enhancement for MGM to garner even more men to listen, and hopefully listen more during the week. It would not compliment say, WFPG, because it doesn't serve the station's target of women.
And because the NFL plays so few games, they prefer their franchises on big signals.
If another music station, specifically rock, like WZXL could get their hands on it, they too would drop music for 3 hours a week, for the ratings and revenue the NFL brings. Also, the games disturb little as they are usually played in what is normally off peak weekend afternoon and evenings.