Don't you think the main reason would be to fit the dispatch program to fit the needs of your operation? If Delta is really charging those attending their program $2,000 like others have said, they certainly aren't making much money off of it. Especially if everyone within the program has a job waiting for them.
Delta only cares about one thing and they're damn good about obtaining that one thing. Money. If DL can make an extra penny off of their employees they're going to do it. The school costs nothing to operate as the instructors are dispatchers on special assignment to teach the course so they're not getting paid any extra salary for doing so and they were going to pay the prospective dispatcher the same salary that they would have had to pay any other candidate.
The internal push came about from a mandate that 80% of "advancement" opportunities were fulfilled from within. I use quotes because although our jobs are very high paying and carry an enormous amount of responsibility, it is still technically an entry level position. I can walk into any regional and most mainlines right now and become a dispatcher without having to have thrown bags for them.
Previous posters are correct though, it seemed for a fleeting year and a half that Delta was coming out of its shell and seeing the benefit of external hires with dispatching experience. However, that door was slammed shut in the past year as 76% of the hires since January 2015 have been academy grads. 2016 has been 100% internal instead of 80%.
I guess it's easier to brainwash people who 8 weeks ago didn't know what a dispatcher was into towing the corporate fuel line rather than an experienced dispatcher that knows when tough decisions have to be made and acts in the interest of completing the mission instead of economy.
@manniax, This push doesn't have potential to hurt Connection carriers, it IS hurting connection carriers. I personally know 15 strong dispatchers that were at various DC carriers and wanted nothing more to come bask in the ATL summers. Of them, 5 had a chance to come test when it was still ok to go outside of the Delta Garden and either chose wrong when deciding if they'ed rather kill mom or dad or couldn't do enough correct currency conversions. All 15 are now working at UA, AA, B6, and WN.
The cherry on top of all of this is that Ed recently responded to a question regarding Delta sponsoring training for internal candidates that wanted to become pilots. He said no, because there was lots of talent out there that would want to work for Delta and they (Delta) would have their pick of the best. Odd that that logic does not extend to dispatchers as well.