Because they invested billions of dollars into making said devkit and despite seeming promising the actual general usefulness of it was still extremely unclear, so it was down to 2 choices: a) kill it, or b) ship it and see what happens when the rubber meets the road.

Arguably Apple has never done b) before, but then again they’ve also never poured billions into a R&D project like this before. (The only other example that comes to mind is the car, and that one got killed, so maybe they were loath to kill the two billion dollar science fair projects at the same time).