I did not read through all 5 pages of response, but I think delaying the release of the GECK is a simple business strategy.
It is possible the mods made with the GECK (no matter how small or large they are) could distract a few players who are looking for new content to play with from immediately purchasing DLCs. Therefore, withholding the release of the GECK means that more players would be focused on the paid DLCs rather some potentially good free mods.
As others have stated, the GECK is more of a gift than anything else. It is something that Bethesda provides to the player community that will keep them interested in continuing to play FO4. In a sense it is kinda like Christmas. Gamers know that the GECK is going to be released just like how kids know that they will be getting presents from their family for Christmas. The difference is the kids knows when they can open their presents while FO4 players do not know when the GECK will be released.