Walking Dead, Outcast, and Invincible have all been pretty regularly released. Can't say I like the Saga breaks, but, whatever. Honestly, I think it's the incorporation of the Outcast show that brought on the schedule change. I don't think Kirkman has been writing the scripts forTWD, I just think overseeing everything is taking its toll. The money that Invincible is bringing in compared to TWD powerhouse franchise is probably completely insignificant to Kirkman.
EDIT: I do have to reiterate how much I would love a properly done Invincible show/film