There were a lot of different genres in the 90s. This was a problem for Top-40 until the late 90s because there was a lot of fragmentation.

Alternative was massive in the 90s. Hip-Hop was massive in the 90s. The Early 90s had the Dance, New Jack Swing sound. Then there was the more Modern AC sound in the Mid 90s.

This was an issue with some stations not wanting to play Rap and alienating their older audience. Even some Urban stations didn't want to play rap at the time. Some stations also didn't want to play harder rock (Alternative) thus Hot AC came to be a thing.

For the remaining Top-40 stations, most of them in smaller markets, some leaned toward Hot AC, some leaned more Rhythmic (B96 is an example) some leaned more heavily on Alternative, others where there was not a specific station for every genre, particularly smaller markets kept it somewhere in between.

Artists like No Doubt, Nsync, Britney Spears, Paula Cole, Celine Dion, Jennifer Paige, Hanson, TLC, Barenaked Ladies, Brandy, Monica, Sixpence None The Richer, Ricky Martin, Whitney Houston, Sugar Ray, Destiny's Child, Will Smith, Madonna, Third Eye Blind, INOJ, Next, Matchbox Twenty, kept pumping out hits that brought the genres together again. Pop, Rock, Hip-Hop, R&B, some Dance that blended together again. Really brought the Top-40 format back again.

After 2000, particularly after September 11th, the pop aspect started to disappear and the Top-40 format was pretty much either Hip-Hop or Rock. Not much in between.

I feel if stations play 90s (or any decade) it should be market specific based on what was big in the market at the time, but it would be too much effort for the larger companies that run everything based on a single log. That might be a reason why there is not much 90s. They're not researching every market, don't want to bother. They just test what already tests and tested in most places and don't bother to go any farther.

I feel it should be more market specific with 90s music