Writing woes

I really wish I could learn to work on one story at a time, exclusively. Instead, I am currently writing Terminus (my canon-compliant TNG fic), the regularly scheduled next part of Torchwoodgate, the Omegaverse Torchwoodgate story that isn't due for a long time yet but I got inspired, I was bitten by an Enterprise AU plotbunny, of all things, an theoretically still have Kansas 2 on my list.

Why has my brain to work so irrationally?