Like telecomm, wifi, and USB standards, web browsing protocol standards are deliberately overcomplicated as a way to legally fend off competition. Anytime a big corporation gets its hooks into a Standard, one can expect its complexity to grow forever unless an individual at said corporation prevents it.
IMO, it's more that the standards are overcomplicated as a result of (unhealthy) competition. This is maybe less true now, but my impression has been that until recently, Firefox and Chrome were both always racing to implement some new proprietary feature before the other browsers could design an equivalent. There were no standards. In fact, even before that, the way JavaScript was created is that Brendan Eich, at NetScape, implemented it in two weeks. The same was true of many other browser features, they were rushed into production in order to outdo other browsers and have this new feature first, and then everyone was kind of stuck having to support every half-baked feature because some websites made use of them.
It’s probably not so much deliberate complexification, as reluctant simplification. The system will become complex all by itself when there is little pressure to streamline it.
Truly, while the web also now being better than at the time of activex and flash etc. I’d wager the only rescue for a new free non-WebKit would be simple ways to use external programs - maybe yet a challenge for language design.
