Hopefully is the best answer!

For one of two reasons:

1. The airline in question is growing and is now able to re-accept their heavy routes and let the CRJ's do what they were intended to do - serve the smaller cities that couldn't support a bigger aircraft or farm the new cities until they reach larger aircraft status. Since 9/11 - the RJ's have been used to lower the costs of operation for some "light" routes.

2. The more 737's that take over CRJ/ERJ routes the better chance you have to make it out of the RJ's and land at a major. The better chance for the industry to return to higher salaries also exists with this model.