It's about market saturation and the ability of ownership to diversify their assets within a given market. 102.9 (Buckley Broadcasting) recently flipped to classic rock and Hartford isn't big enough for multiple stations of that genre. It is similar to why 104.1 (clear channel) flipped 10+ years ago from modern rock to hip hop. Between them and WCCC (Marlin), there wasn't enough listenership to go around. Then more urban stations showed up and again you had over saturation. WCCC began to change away from modern rock, without the total flip, and 104.1 went back to rock, yet different enough from WCCC to account for two stations. In the meantime, smaller ownership groups were selling these stations off and/or the large conglomerates (clear channel) were pulling the strings, forcing these changes. It sucks for the listener but it is a business for the ownership.
Boston, the ninth largest radio market in America, basically had four rock stations about five years ago, WBCN, WAAF, WBOS, and WFNX. All were different enough but even in a market that size, there wasn't enough listening audience, and as a result advertising dollars, to go around. Mix (top 40, owned by CBS) moved to BCN's frequency, FNX (owned by Boston Phoenix) was sold flipped to techno and has recently flipped again to country, AAF (Entercom) has more or less stayed the same but with an emphasis on harder rock and 80's rock. WBOS (Greater Media) moved from lighter AC/rock stuff to more 90's and early 2000's stuff.