Well, brief history... uGUI started as NGUI. That is, I took NGUI in its entirety and branched off from it to create uGUI. There was no deal or compensation, I just felt that Unity deserved a solid foundation to start with. That was around April last year. From that point up until mid-June I was on it mostly by myself and had full control of what was being changed.
Eventually other people jumped onto the project and things started getting pulled in other directions. Rendering/batching pipeline, complete inspector re-design, scene view handling, text system, anchoring system... Some changes I liked, others -- not so much. In the end I felt like I was also pulled in different directions. On one hand I wanted to finish uGUI, but on the other hand I felt that I had less and less control over the overall polish, and I found it frustrating.
I also wanted to do game dev because I passionately believe that in order to make great tools, the people making them have to use them as others use them. Unreal has Gears of War. CryEngine has Crysis. idTech had Doom and RAGE. Even Unigine had Oil Rush. Unity... has nothing. And it shows as a bunch of half-finished systems that devs have to work-around.
Cloth crashes Unity if included in prefabs, doesn't respect rigidbody interpolation and can't be disabled without breaking. WindZone not being available to scripting at all. ParticleSystem not having most of its properties exposed to scripting... Those are just the ones I encountered in the past week alone.
I hate hacks. I hate them with a passion. Seeing things come apart as others started changing them, and become visibly worse with the excuse of "oh, I'm just going to get it working for now, make it pretty later" wore at my resolve. I believe that if something is worth doing, it's worth doing properly, and from the start. Because let's face it, most of the time there will never be a "later". Once a feature is in, devs will move on to the next thing. Polishing, and more importantly -- using those features is never a priority.
In the end, I realized that I was spending a lot of time idling, and very little time actually doing something. My "mojo" was gone, and I wasn't going to stick around for the paycheck. And so I left.
Curiously enough, my mojo returned within a week. I was back at it doing dev work, and the week after my last week at Unity was the most productive NGUI-dev week I've had to date, with me adding many of the features people were asking about.
Now it's a new year, and I am focusing more and more on game dev, which is what inspires me in the first place.