C major is only easy conceptually, technically other scales are easier, such as B major. In guitar transposition is easy conceptually, but not so much technica

C major is only easy conceptually, technically other scales are easier, such as B major. In guitar transposition is easy conceptually, but not so much technically, not being able to rely on open strings as much is a big limiter to novice guitarists. And guitar being such a popular instrument, there's a lot of those. On average technical limitations will dictate keys more than conceptual limitations.