I don't quite understand your post.
WOGL, is #4 with Oldies (I'll not argue that for my ear WOGL repeats too many songs and plays too many Motown and Soul tunes in relationship to all the other music being played on their station, but when was the last time WOGL was in the top 4? So apparently someone in Philly likes what WOGL is playing and is listening, and even more importantly are in the magic demo advertisers want. Remember radio is a business. If CBS radio thought they could capture the #1 spot in ratings and magic demo, etc, in Philly by airing Polkas, believe me, they would.
So if you want to hear a more traditional oldies station the Vineland WVLT might suit you better, but they don't get as solid ratings and more than likely skew to an older audience that the advertisers do not want. WVLT might be able to make a go of it in Vineland NJ, but probably would lose their shirts in Philly, which is why WOGL doesn't play what WVLT does. Even though I personally would prefer a more traditional Oldies format, I also understand dollars and cents and realize that CBS radio is in the business to make money.
WXTU has done quite well doing Country, of all things, in a Northern Rock and Roll city like Philly, who would have thought 40 years ago that country could, much less would, being popular in Philadelphia, the home of the mummers.
Jazz is alive and well as also is Classical Music on WRTI, which has done so well as a non-comm they have repeaters (two in Delaware - Wilmington and Dover), plus a boatload of them in PA and NJ. More people in the Delaware Valley have access to Jazz and Classical Music than ever before.
I do hear some Mexican music on some low powered AM stations, WNWK 1260 Newark DE, plus I believe it is 1280 in Georgetown DE. I guess there is some Mexican or Hispanic music on stations in PA and NJ, I've just never come across them, but even so, what's the big deal. That's what America is all about. If there's a market for Mariachi Music why wouldn't some station jump on it.
If the music is popular enough with the magic demo advertisers want, then you'll hear it on the big commercial radio stations, if the music isn't popular with that magic demo, then you'll find it, more likely, on a non-comm NPR station or a non-comm College station, where people vote with both their radio dial and their wallet. It ain't perfect, but it does work.
One final comment. You seem upset by hearing minority music at all, better get used to it as the Census folks have said that by the years 2040 to 2050 the white European group will become a minority in the US. Like it or not, due to immigration and the fact that white families have had far fewer children during the past 50 years while the minority families have had more children has caused this change. It's not the end of the world, it just will be different than it has been before. Sure cultural things will evolve as the former minorities become the majority, but that's how business works. Radio and TV will surely be affected and will go more towards the majority listeners (the former minorities) and viewers choice for music and entertainment. That's simply good business.
Go back to the turn of the 20th century when Irish and Italians were streaming past Lady Liberty and there were probably some then who felt that Lady Liberty and America would be hurt and destroyed by all those folks who today are part of the mainstream. America kind of works that way. The Irish and Italian customs, music, food, etc, are now part of our American heritage. Who things twice about going to an Italian Restaurant or an Irish Pub. People flock to Wilmington, from all over the Mid Atlantic area, once a year to attend the Italian Festival at St. Anthony's Catholic church. So some day, we'll flock to a Hispanic Cinco de Mayo festival with Mexican Music, food, drink, dancing, etc, as those folks will be part of the mainstream of this nation as America marches on. Radio will adjust just as it has since its beginnings in the 1920's to meet the business needs of advertisers.