I don't understand why insurance companies are not mandated to have a single pool of insured - ie. per company. Why should individual health be a separate pool from group insured? The delta risk per individual is much lower if the pool is larger.
Because nobody would pay the rates that it would cost if they had a single large group. How many healthy, not-currently-pregnant 25 year olds would sign up for health insurance at $400-500/month? If they won't sign up now for $100/month, I'll guess that the answer would be not many...