Maybe it would have been better if you asked: "Why are people using modern / late generation SLR's instead of going with a 10 dollar 25 year old one you can get on E-bay?", because I have the feeling, this is at least partly what you are asking.
Well, for me and my Minolta Dynax 7 (yes, the film one):
- No broken light meter or other end-of-lifetime electronics that might let you down.
- Ability to use modern NiMH rechargeable batteries
- Lighter rugged plastic / metal combo (I don't need a full metal tank that breaks my neck)
- Lot's of bells and whistles I like:
* Fantastic well lit status display on the back, great for night time photography showing a BULB exposure time counting up.
* Exposure data memory storing used shutterspeed, F stop, focal length etc. for up to 7 films, no worrying about writing it down...
* Ability to transfer film data to my computer (yes, I am still talking an analog camera, or should I call it "hybrid" )
- And more I like...