I don't think the users decided on anything. Browsers are just prone to insane feature creep as a result of the game theory involved.
If you are a browser vendor, you don't want your browser to not support a feature that other browsers don't. Otherwise, users go to a website, and it doesn't work properly on your browser, and they blame you. If this website is something important like a bank, a news website they like, anything popular that their friends use, they might well ditch your browser. As a result, to some extent, browsers have to support all the features that other browsers do.
On top of this, browser vendors want to remain "innovative", show leadership, so they keep pushing for new features that other browsers don't have. I mean, imagine working on some browser team, having the opportunity to push your web project and having it become a standard web feature, your legacy would live on forever, the hubris of it is just irresistible. Fuck taking the time to properly design this API, think of possible use cases, and design something solid and extensible, let's push WebVirtualReality2000API out before other browsers do, otherwise they will push theirs first and start gaining traction!
So, back to JavaScript. Brendan Eich worked at Netscape and implemented the original version of it in two weeks and it was rushed into production. People started to make use of it. Eventually other browsers had no choice but to support it, otherwise they were faced with lots of webpages that were broken without it, webpages that only work in Netscape. Microsoft definitely couldn't let that happen.