People talk about big corporate radio as though it didn't exist before 1996. But ABC Radio was big corporate radio in its time. Amazingly they did a fairly good job with FM in all of their markets except San Francisco. From what I've read here, I gather the blame should all go to Mickey. He didn't see it coming. He and Sklar had their heads firmly in the past and couldn't imagine any use for FM.
There were lots of broadcasters who just could not see FM happening.
Storz, without the vision of Todd, never looked seriously at FM and they sold the stations about a decade after his death.
Storer, one of the largest independent operators, sold off some FMs and did not develop others rapidly. In the mid-70's they were busy upgrading KTNQ in LA on AM instead of moving into FM.
Taft eventually developed its FMs, but was slow.
Metromedia, under Kluge, was an early adopter of the post-simulcast-prohibition opportunities with his Metromedia. Think "Buzard".
Golden West / Gene Autry did not develop FM rapidly. Doubleday, even under Gary Stevens, was focused on AMs; when Stevens went out on its own, he quickly looked at FM for growth.
Bonneville adopted its own Beautiful Music formats, so it was "big" in FM but did nothing further for years..
Those are just a few examples. But FM took many by surprise when one or two operators "opened up the band" and "brought down" established AM stations, sometimes very fast. I saw one top 20 market go from 12 FM shares to over 50 in less than 6 months.
ABC inherited a great combo from Star in DC and managed to do a great job with the combo, making WMAL-FM into a powerhouse Q107. It was a consistent ratings winner for years.
But that was a late arrival on the list of early successful FM stations. In DC, the station that broke the band open was WPGC, which had an AM daytimer Top 40 but upgraded the FM and immediately knocked off WEAM and other contemporary AMs. That was right about when we landed on the moon... a very early "big" FM. But it already found good Beautiful Music stations on FM, and even the first real FM "oldies" station, WMOD.