A lot of the choices were to be fair quite accidental. Computers didn't use to be like this, but a lot of the reasons they weren't were properties of how the technology worked. A low-DPI 15" CRT monitor simply can't display very much information at any given moment. A slow single core CPU just doesn't permit browsing the web while your code is compiling. As that changed, we simply piled on multitasking capabilities without asking if we should.
But yeah, it's an interesting space to experiment in. I feel we could be doing much of this a lot better than we are now. My mise-en-place work accounts is very much a hack, and considerable work to set up.
Oh 100%.
On their own, browser tabs, notifications, and IM at work all make sense on their own and are not evil at all.
Taken together, there are now 8 people trying to talk to me all day every day, constant alerts unless you go out of your way to severely restrict what and who can message you, and you find yourself with 60 tabs across 3 windows doing 7 things at once but also doing nothing because... your brain was not built for this computer.
Before 1992, we browsed newsgroups, watched TV, or played with swords while compiling. That is, if you weren't using Turbo Pascal, with its near-instantaneous turnaround.
https://xkcd.com/303/