This is one thing I've always either overheard mentioned or seen pointed out to people who bring up or show interest in the Pentax brand. I thought this was interesting to actually see. The site below shows the most popular body and lens combinations culled from online picture data.
Cameras + Lenses
In this particular case, the results indicate that many users in the Nikon and Canon (FF or crop) camp do not necessarily circulate through their large libraries of available lenses. Which makes sense, because why would you (working professionals aside) just hop from lens to lens if you find a handful that cover your desired focal lengths, and please you optically?
This visual realization is not surprising to me, as this was always something I thought to myself when someone would highlight the "issue" of limited lenses for the K-1 as a reason not to switch or try it. While technically true by comparison, and more lens options are needed overall, is it really that big of a deal if people are real about their needs? The majority of focal lengths used for all the listed bodies are covered in some fashion in Pentax's library for either format, so a large chunk of other system owners would be just fine over here if that was the most important deciding factor for them.
It seems that most everything that people buy these days is bought based on like of the idea or potential of capability of a thing, and not whether they plan, are capable of, or even deep down have a true desire to explore it.