Can you list any examples? My hunch is that there are good reasons javascript is included on most sites where it is found.
Some of the incentives fueling this trend could be viewed as undesirable (e.g. monstrous ads on news sites as a desperate bid for profitability), but that doesn't negate the fact that the incentives exist, and aren't simply "people love over-complicating stuff".
Most of the web is so-called "content". Formatted text, images, video, audio. These require very little interaction. If you don't have user interaction and are just serving content, you probably need very little javascript. So I would say most major news sites, weather sites, etc. are examples.
To illustrate, hacker news and reddit work fine with javascript disabled, and the javascript they use is simple and just makes some interaction like voting work nicer. Even amazon, which is a pretty bulky and interaction-heavy site, works quite well with javascript disabled.
As for incentives vs over-complication, there's an interaction there. The incentives are to put some fancy whirly whingding on your website because it looks flashy and your target audience has (according to you) fast internet connections and web browsers. The incentives are to do this with the minimum of effort even if that means serving multiple-meg, javascript-heavy pages that don't even have any interaction.
Some of the incentives fueling this trend could be viewed as undesirable (e.g. monstrous ads on news sites as a desperate bid for profitability), but that doesn't negate the fact that the incentives exist, and aren't simply "people love over-complicating stuff".