People collect all kinds of things. Old cell phones. Funko pops. Sneakers. Coins. Cars. Minerals. The list goes on and on. I wouldn't be surprised if, when the very first ancient smoke pole was produced for the commercial market, the same guy that bought the inaugural model came back the next day to see if there was a new and improved version for sale. Thus began the tradition of gun collecting, or so I theorize.
Today, there is any number of reasons to acquire a firearm-- for sporting uses, personal defense, and as cherished passed-down family heirlooms. It is also standard to get them "just because." Once you have more than one, you are on the road to being a collector, which can take any number of avenues.
It is up to the budding collector to decide what they want kind of guns to fill their safe with, and that is one of the most American things ever stated.
You can carry this on to calibers-- only collecting .44 Magnums-- or styles-- collecting single-action revolvers of the Old West era only-- whatever. I know at least two different people who try to acquire guns manufactured the same birth year as them.
Guns with long factory runs will have numerous generational engineering changes to improve the firearm and make it easier to produce. For instance, the Glock 17, which has now been around for 40 years in continuous production is on the fifth Glock-declared generation while collectors recognize several different incremental variants as well. The S&W Model 10 is on its 14th generation since 1957.
Some collectors who really like a particular model often grab one of each variant, or try to, and such sampling can really illustrate the factory changes over time.
On otherwise collectible pieces that are not in "mint in box" condition, there is nothing wrong with minor updates that do not permanently change the firearm, coupled with occasional range visits to fully enjoy the gun. Just be sure to save any of the original parts that are removed so the gun can be "reset" down the road if desired.
A durable piece of history, firearms can often carry a story of another time and place, frozen in history as much as a prehistoric fly caught in amber.
Guns can also be collected due to a familial connection to a historical event or period.
Current events can often be a boon to collectors. A sort of Newton's third law as applied to the firearms market if you will.
For instance, as a side effect of the thawing of the Cold War after the demise of the Soviet Union, the mid-1990s saw Russian military surplus firearms flood the market at prices that would make you cry today. Mosin M91/30s for sale by the crate (20 rifles for $1,100), complete with all the accessories. Nagant M1895 pistols, with holsters and cleaning tools, for $49 a pop. Tula-marked SKS-45s with early 1950s production dates for $99. This leads to the easy argument about investing in firearms.
The important takeaway if you find yourself in a similar market:
While they seem almost too inexpensive at the time to waste precious dollars on, once the supply dries up for whatever reason and the going price shoots up, any would-be collectors who missed out can do in later years is shake their heads and moan about how they "shoulda got one when they were cheap."
In the end, gun collecting is a natural part of human nature, at least in a free country, anyway.