Entry into an orchestra isn't something that is cost prohibitive for an economic class of individuals.
Applicants to orchestras likely enjoy a certain level of affluence given how demanding the required practice is for performers. Musical performers enjoy slightly less systematic discrimination throughout their careers and technkal musical ability is something that is largely self-taught meaning that the applicants to orchestras are more likely to share similar levels of abilities at the stage of auditioning for an orchestra whereas college applicants are more likely to express difference at the time of application due to systematic discrimination throughout their educational trajectory.
Playing in an orchestra doesn't share the same grave weight of attending college in careerist society where college is increasingly necessary. The demand is higher for college, and the supply can reflect that.
Orchestras arnt a part of a massive industry tied to sports, science, defense, state subsidies etc...