SDK's, in general, require a full team to manage, test, QA, etc. And usually take an inane amount of work to maintain. I think I'd rather they work on making sure the game is good and solid before diving into things like SDK's. One of the reasons why the GUI has so much effort put into it is that so we don't need SDK's for the GUI.

What it really comes down to is this: average players won't care enough to use it. Programmers won't let the lack of it stop them.