People need new technology and features in their website, business demand them to make things look professional and easier to develop.
But that's not the problem here. The problem isn't the things that Javascript
is needed for, the problem is all the places it
isn't necessary but gets used
anyway. Modern web developers are so stuck on fetishizing glitz and flashy animation and such that they don't ever stop to think about whether it's necessary, and it usually isn't, or whether it impairs usability, which it often does, or whether there's a simpler alternative, which there usually is. (If I had a dollar for every time I've seen JS drop-down menus when CSS has been able to do that since
forever, I'd be a significantly richer man.)
(The further irony is that all this often actually looks
uglier, in a trashy disco drag-queen kind of way, than the simpler alternatives.)
Hell, we're even getting to the point where it's common practice to reimplement
basic browser functionality like links and the back button in Javascript, often in ways that break the
real in-browser implementation.
That is Bad And Wrong. This is not a problem of old technology not keeping up with the requirements of real improvements in web design, it's a problem of
bad design becoming the rule on the web.