The problem with a maximum wage is deciding what that maximum is. Outsides returns are what incentivize people to start companies. A earning cap will cap that incentive accordingly.
If you rent a $10m house you pay $500k a year for it. With 50% tax you'd have to earn $1m a year to pay the rent.
If you own a $10m house you pay no rent, and have to earn $0 a year to live there.