I used to wear your shoes in IE6/7 ages (no longer, I gave up during the "framework of the week" race and went all-backend), and it wasn't simple at all. Browser compatibility with all their rendering nuances, individual system oddities and all sort of fragile stuff.

And fortunately, no one bats an eye at a slightly broken site, but everyone hates even a slightly broken vehicle.

It's simple because we tolerate certain limitations in the web platform.

If you had a hard requirement that a page load could never take more than 100ms, regardless of network conditions, you'd have quite a challenge on your hands.

I'm not really a frontend dev any more but I was for a long time. I can assure you that the only reason you think your code works is because no one tells you it's broken. If you use an error logging or telemetry service (Sentry, Rollbar, New Relic, etc) you will be aware that errors happen in frontend code all the time. It's just that most of the time bugs don't crash the app, and the user doesn't know what to expect so they see a broken feature and think it's meant to be like that.

I don't think it's fair to consider the updaters for either Chrome or the OS to be simple.