[Santosh83]

It's the rise of Chrome and web as an app delivery platform instead of just interlinked documents. This has necessitated a huge, ever expanding API and ever-increasing security concerns, and these have totally swamped browser devs to the point that they have simply stopped caring about end-user UI, productivity, customisation, backward-compatibility and such.

The web is now essentially an operating system under active, nascent development, so the churn is going to be enormous and the whole thing will lack any kind of polish or UX. Expect it to stabilise in a few decades as something else takes over (maybe).