Hardly a Zep-only problem is it? I assume you’re listening to a commercial station and they do this with every band. If you are young and get your musical history from the radio, you would think that Faith no More only did “Epic”, Sabbath’s only single release was “Paranoid” and Jane’s Addiction were a 2003 one-hit-wonder with “Just Because”.
Perhaps in the Zep case, it’s to do with short attention spans and intros – I’d agree that Ramble On in its entirety is more radio friendly, but it properly kicks in at the first chorus, with a so-so intro. Whereas the first three seconds of Whole Lotta Love is one of those “Yeah!” riffs..