User expectations, or executive expectations?
In my experience, the effective expectations of users are remarkably low. If you were to survey users, you'd get the impression that users are very particular. In reality, users tolerate all sorts of things that most of us on HN would consider primitive or nearly broken. If most web applications actually relied mostly on constructs provided by the browser/DOM rather than JavaScript, the average user wouldn't notice or care.
But there are product owners who power trip on the possibility that they too could be just like The Google, so they want everything to be unnecessarily animated and dynamic. On top of that, many of them want Silicon Valley programming at San Fernando Valley prices, so not only do they request that their web applications be unnecessarily complicated, but the junior devs they hire are given no direction and the code gets bloated, wrecking performance (which matters more than "delightful" UIs).