Because it's what I played growing up, and it's one of the most fun experiences I've had with my siblings back then.
The chaotic energy of the battle mode, especially when you would be one of the first ones to lose and turn into a bomb, was so much fun!
I've played Mario Kart 8, and I think the new characters and items are really fun. Everything is so wonderfully detailed, though, that my dumb ADHD brain sometimes forces me to stop and see all the cool details on the tracks. Lol
64 is my fav. I often played it with friends in college. Grew up with it. Had the best memories with it.
Double dash is in second. Spent hours with friends on baby park trying to fill that map up with so many dangers. Pure Chaos.
Nowadays, I'd still choose 8 if I was hosting a kart night with friends though, because they haven't overcomplicated it too much yet and it still has the same charm.