What has stopped the 737s so far has been the union. The current Mesa contract (like most other airlines) spells out the payscale for all aircraft in inventory. It also has a provision that specifies that management can create basically whatever payscale they want for new aircraft...HOWEVER this payscale is temporary, and will be re-negotiated at the next contract. It is very likely that the new negotiated payscale would be retro-active. This essentially means that the company cannot devise a business model for new aircraft without the pilot's agreement because the true costs are unkown.

As to why you would stop them...if you can get industry standard pay & benefits, there's no reason to stop anything. But that's pretty unlikely to happen at Mesa...most of the pilot's have no interest in flying 73's for RJ pay and undercutting mainline.

There are always a few senior career regional guys who would be willing to do it though.