So I guess the question is, how do we ensure that only experienced professionals inhabit the cockpit of airliners?
Easy, pay them properly. Offer a good benefits package, decent working conditions and have a good relationship with them.
Regional airline flying can offer a better lifestyle than the majors and suits some people who may wish to live in a regional area and/or be home every night. A 45 year old may not want to go back into the right seat and wait years for an upgrade while having to learn an new type and a new operation.
SAAB 340/DHC8 captain with a good package and coming home at lunch time would appeal more to a lot of older pilots than 10-14 over nights per month and back of the clock operations.
There will always be turnover in the regionals which is a good thing because it provides opportunities for others wishing to move up the ladder. Looking after the experienced pilots who want to stick around is in everyones interests.