Comment by iamcalledrob

The root cause of this stuff, from experience, is that animations are hard to retro-fit after the fact. It's a lack of planning.

The UI code needs to be structured with animation in mind, with hooks in the right places. And to do that, you need to know what is likely to be animated together.

But what ends up happening is you encapsulated a few of the moving pieces in abstractions (e.g. "toolbar", "sidebar"), but you want to animate stuff within. You end up copy+pasting animation logic inside each (now leaky) abstraction and duct taping it all together. UI abstractions are hard!

(Yes, on apple platforms there are transition blocks which will capture changes to the entire view hierarchy, but then the battle becomes preventing animations on stuff that shouldn't change!)