2. There is license requirement, taxi medallion like setup with lawyers, doctors which keeps overall supply low.
3. It's just not just your salary which company pays. There is a cost to company per employee if the ratio of your salary: cost to company declines, you are a problem for the company and company wants to invest in an employee with a better ratio.
Also, you are making an assumption that we can look at an employee's productivity in isolation.
No, there is a guy at our company. He is good at everything he does but no one wants to talk to him at a company due to his behavior issue. And whenever anyone finds a work which needs talking to him, they drag their feet, make excuses just to avoid him.
Maybe older guys don't fit in the band of recent graduates? Maybe they feel that new guys are reinventing the wheel and dismiss the idea outright?
Just imagine, if someone experienced (or old) (who has years of experience in payment processing) told Stripe founder that their idea is BS because they are tired of payment processing and have seen nothing new.