Ask HN: Why does any program I run have access to my browsing history?

When I run a program as my own user it can read anything from my hard drive. It can read my browsing history, look in my Documents folder where I keep important personal files, etc.

Contrast this to a web app, which has very strict default security settings implemented by my browser.

Why does this kind of sandboxing seem to be of major concern to my browser, but not my OS? What's the history that led to things being this way? Why is it still the case today?