In my opinion, an accurate description for this phenomenon is "atrophy." If muscles go unused for too long, they begin to fail in carrying out their proper function, for two reasons. Physical weakness, and a loss of muscle memory. In the case of musicians, our primary concern is the muscle memory, since fingers typically have adequate physical strength for our purposes.
I believe that this concept of atrophy applies to other musical skills, as well. The less we explore our skills, the less we can count on them to stay at a usable peak. Beyond technique, this applies to all manner of songwriting and theory as well.
With the increasing number of bands who prefer to release EPs as opposed to LPs, there's less of a requirement to create a diverse lineup of songs to fill an album. The demand is, as a generalization, cut in half when one opts for an EP. It's not much of a stretch to assume that the ability to fill an album with a varied collection of songs could atrophy as a result.
If you find yourself struggling in this regard as well, there's a very simple way to begin rebuilding that ability. There are two pre-requisites, however.
First, you must be aware of your band's "main" genre. For example, you may be versatile enough to write a jazz song, or some folksy instrumental sections here or there, but your band's genre is marketed as "metal," therefore you know that the guitars and drums will likely be a linchpin of your band's sound, regardless of what other elements you add in the name of variety.
Second, you must have written at least one song.
With style and a "first step song" underway, simply look at that first song, and decide what it does not feature. To give some extremely clumsy and over-the-top simple examples: If your first song features primarily grooving drum beats, try adding some blast beats to your next song. If your first song features a lot of palm-muted power chords, try some more mobile single-note riffing in the next. Use different synth patches, if your band features keyboards. Use different gimmicks - maybe one song features many different time signatures, while another features polymeters. There are endless areas of difference you can emphasize to avoid being one of those musicians who has to hear that "all your music sounds the same."
For a more in-depth discussion, take a look at the following video:
Let me know in the comments how you guys feel about this idea. I hope it was helpful to begin thinking of how to add some versatility into your compositions.