It's more easy to understand that web sites are doing it but i'm not sure what is the reason on Desktops where you can open multiple window.

I once wrote an application with a Settings Topmenu and then as submenus the items which now always implemented at the left side in a icon list/tree. I liked it my way much better (it was a large program with lots of settings) and sometimes showing two different settings pages at once even turned out to be pretty convenient.

But it's so extreme mainstream now, i hesitate to implement it my way.

It's easier understand why web sites are doing it, but i'm not sure why desktops place settings in one dialog when, for example, multiple windows can be opened.

I once wrote an application with a Settings Topmenu and then as submenus the items which now always implemented at the left side in a icon list/tree. I liked it my way much better (it was a large program with lots of settings) and sometimes showing two different settings pages at once even turned out to be pretty convenient.

But the single-dialog settings box is so mainstream now, that I hesitate to implement it my way.