The short answer is longevity, these cadets are more likely to stick around with the company that trained them and introduced them to the business, regional pilots (specially in the US) have been so mistreated by the industry that they have very little loyalty to any particular company/organization, they have been exposed and well versed into the ins and outs of the negative side of the union and although very experienced in bad weather, cold WX operations and complex air spaces, there is also some baggage there (not all cases of course, I know many guys that are extremely professional and that are looking for an exit to the rat race) so they don't want to be a means to resume boosting so that their application at Delta, FedEx looks better.