If it doesn't and you just buy guns you think are cool or for specific uses, more power to you. Not all gun owners are collectors, and don't have to be.
For people that think of themselves as collectors though, I think it's helpful to establish a theme, otherwise you're just buying guns (again, a totally acceptable thing to do) rather than building a collection.
Some cool collection ideas I've known friends to be working on:
\- Every US service rifle from the foundation of the country.
\- Primary small arms of specific conflicts (World War 2, Cold War, etc).
\- All guns from a specific manufacturer (I feel like HK is the brand I most often see this attempted with).
I decided I want to start a collection that feels a bit nerdier (besides also aspiring to some of the ones mentioned above, like US and WWII service rifles), and I personally want to own every gun from Counterstrike as part of my collection.