Also: off road/overlanders. Stock parts just don’t work.
Edit: I have replaced diffs, springs, shocks, tires, wheels, and added a steering damper. For overlanding that is pretty minimal work. For Motorsport style off-roading, I would need to do quite a bit more.
I was about to chime in with this, but you beat me to it. (HZJ79 Land Cruiser, lockers rear, center and front, full underbody and steering protection, expedition tank, water tanks, upgraded shocks, the mandatory snorkel, a real mother of a roof rack, steering damper coming up...
Sigh. Any hobby you can get blokes interested in eventually turns into gadget madness...
I knew someone would mention the Land Cruiser. It's the quintessential car for the HN crowd. It's upscale doesn't have the redneck vibe like an 80s Bronco or Suburban does.