Because people want a desktop application experience inside of the browser.

When I was playing a Counter Strike web app example posted here a few months ago, it was endlessly frustrating to have Control and W mapped to actions that you may want to perform simultaneously while also not being able to suppress default behavior. I kept accidentally closing the tab as a result...

I personally think that the ability to override default shortcuts isn't necessarily a bad thing, but I definitely think it should be opt-in, like capturing the mouse cursor is. There should be strict separation between "app" features and what a default website should be able to do. Overriding shortcuts should be one of the "app-only" features imo.

> When I was playing a Counter Strike web app example posted here a few months ago, it was endlessly frustrating to have Control and W mapped to actions that you may want to perform simultaneously while also not being able to suppress default behavior. I kept accidentally closing the tab as a result...

So play the native version - problem solved.

This drive to accomodate people misusing the web for apps just bloats browsers (making it prohibitively expensive to develop alternative implementations) while adding tons of privacy leaks and attack surface for exploits.

While I agree, unfortunately we're in the minority of people who actually care about that. The best I can ask for at this point is sane defaults.