[J_cub]

Is there a reason why most people put pegs on their left side and not on their right?

[BigDumbBear]

The general group of people ride with their left foot forward and naturally spin better to their right. There are a smaller group of folks that ride with their right foot forward(known as goofy-footed) and spin best to their left. Those things are also related to how easy it is for you to grind on one side versus the other. Wich ever foot is more natural for you to have forward is the side you should put the pegs on.

[mts198]

I ride right foot forward, hence my pegs and grinding is on the right side. I know back in the 90s having a large (44 tooth) sprocket was common and riding goof really could damage the sprocket. Some goofy foot people would switch the sprocket and freewheel to the other side so this wouldn't happen.
With the newer smaller sprocket style they have now it isn't as much of a concern