In short, I was simply more comfortable with Sparrow.

I think it was a combination of a bunch of factors. I was learning iOS development at the same time as I was learning cocos2d, all while brainstorming and hacking on my first ever mobile app. Thus, every time I couldn't remember / figure out how to do touch handling, or place a sprite at the correct location, etc... I blamed it on cocos2d. :-D Of course, cocos2d is a fine toolkit. Just see how many games people have developed with it!

Before doing iOS development, I had spent my 2.5 previous years doing AS3/JS development. Before that, I spent ~6 yrs doing Java development. Sparrow happened to match my mental model of how graphics, event handlers / touch handling, and animation worked.

So if you have a similar background to me, then do give Sparrow a try!