Originally Posted by
Creme Brulee
i always assumed this was because the majority of the population are right handed, so when they pick up the bike to carry it, the chain and chainrings don't brush up against them and get them all dirty
No because it wouldn't be a big deal to carry a bike on the left side. It all goes back to threaded on freewheels, with the freewheel on the right side it will tighten itself as you pedal instead of loosening as it would being on the left.