Keep it stock, or make it your own?

I have only been a member of this forum for a little over a year, but I've noticed that there seems to be more "keep it all stock, all original" guys here than in other forums I participate in. (Except for maybe the Corvette forum, there are some seriously fanatical "keep it stock" guys over there.)
I have never owned a vehicle (car, truck, motorcycle, snowmobile) that I did not modify in some way to make it better suited to me or to do what I wanted from it, better. I'm firmly in the "not-stock" group, and I have been my whole life.
I know there are some rare "numbers matching" low production cars that need to be kept as original as possible to maintain value, but collector cars aside, what would some of the reasons be to keep something pretty common all original?
Don't get me wrong, I have no issues with anyone who prefers a 100% stock original vehicle, and I can appreciate the effort it takes to maintain it that way. It just seems strange to me, and I'm trying to understand the appeal, not cause an argument.

I don't get it either, as I am also a "Do whatever I want to it" person with pretty much zero regard for keeping anything stock.
I did screw up once pretty bad by swapping out the numbers matching 383 Magnum in my 69 Roadrunner and leaving it in a field at a friends house.:D
As far as modding things Dad used to tell me "They did it that way for a reason" and my reply was always "If they would have done it this way in the first place, I wouldn't have to be redoing it".