It doesn’t help that the designers often do not code and model the experiences in animation software.
I am currently working on a redesign and just saw the agency’s suggestions for animation. Seem to be highly influenced by iOS apps’ transitions and motion. But this is a website, for browsers, to be displayed on a variety of screen sizes, on a variety of browser versions.
And the users of my website use mostly other websites so if I create something that behaves very differently, the training they have will be wasted and the experience — unintuitive.
So the agency will present this to high management, in an ideal layout, designed in animation software, moving perfectly smoothly and solving for only one case without a clue on how to approach corner cases. If management finds it sexy, we’ll be stuck with development and maintenance of ultra complicated code. And the pleasure of discovering and resolving all corner cases ourselves, on a deadline, with limited budget.