It is a tool, but some of us collect tools as well.
I collect antique barber razors (straight razors, or cut-throat razors depending what side of the pond you're on). I have one that I actually decided to destroy the value on, and restored it so I could use it as a daily shaver (a 1930s Henckels, I will likely never see a finer blade in my life, and it is one of the most underrated makers of all time IMO). Back to firearms
I feel much that way with antique firearms as well. I like the old steel for it's beauty, elegance and how every aspect of the gun screams quality. Even a 1950s "saturday night special" has a fit and finish that's outright impressive compared to the guns of today. Provided today's guns often perform better, but I'm hooked on the character the older pieces offered.
From an M1895 Nagant revolver's no-nonsense design (ugly as sin, but functions flawlessly), to the Colt Pocket pistol making the Deringer obsolete while still being aesthetically gorgeous, to the S&W K-frame masterpieces and their bright blue finish (with the flutes of the cylinder often aging to a nice warm brown tone to contrast the rest of the cylinder), to the early blackpowder top-break revolvers and their nostalgic charm. I haven't even touched rifles yet....
There's just so much to behold in the world of firearms. Some of us find beauty in function, some of us in form, others in history...but we all appreciate it in some form, thus it's our hobby.
Hobbies are hard to explain to those that have no interest in it. For example, one of my past hobbies (no time anymore) is making period and materials correct exact scale model sailing ships....now try to explain the details for that to someone.