I wonder why most musicians are Earth Ponies with a few Unicorns

[silvadel 1,393]

I mean, other than Scootaloo, you NEVER EVER see a pegasus musician.  When you see a band it is all earth ponies, like Octavia plus three at the gala.  Unicorns are represented by Lyra and Vinyl Scratch.

 

[Spartan 433]

Because earth ponies are built for hard manual work, and being a musician takes alot of work to be good. I assume xD

 

Also, Pegasi and Unicorns use their abilities to get things done, whereas Earth Ponies use their hooves

[Rainbow Dash Loyalty 1,274]

Maybe Pegasus and Unicorns are more busy training themselves with their special abilities. Whereas Earth Ponies don't really have any 'special' abilities so they can use that time into practicing their hobbies (music, cooking, farming etc.)