Because there not long, low or silver (Y)?
The stuff they ride are different for a start, from my limited experience of big group rides with 20/24/26" people is that the the things that the 24" people ride are very different, I'm explaining this crap, hopefully someone will know what I mean, you have to experience it to see it though, you can't really say unless you own a 24"/LLS.
Get out on a big group ride, and see it for you self, hyperthetically speaking, the LLS gang may all have a go at a huge tap etc, while the 24" lot are playing on a bench/wallride (if your anygood, unlike me..) etc.
I agree 100% with what Jonny said though.