When you have 1.6 billion users, every time you waste 5 minutes of their time installing updates and rebooting, that wastes 190 human lifetimes worth of man-hours. I know that Microsoft does not properly account for this when deciding how much effort to allocate to making updates less intrusive.
Most people will not stare at the screen for 5 minutes while it's updating. They will be doing non-computer tasks in the meantime. Also, this ignores the ability for the updates to be postponed[1] until a convenient time (at lunch?, after work?), which means the lost productivity is reduced to the time it takes to restore the workspace.
[1] Even with windows 10's forced updates, I still think it's possible to postpone updates, just not indefinitely.
This is the wrong objection. If only 10% of users lose 5 minutes each, that's... 19 lifetimes' worth of man-hours, which is still excessive. The real reason for not doing rebootless updates is that they're hard to implement, and hard to implement in such a way that they create a risk of problems much bigger than losing 5 minutes (like data loss or security vulns staying open).
But these are not actual lifetimes. You can't kill people by updating a billion computers for the same reason you can't have a baby in one month with 9 women.
When you have 1.6 billion users with such disparate hardware and software, even a small improvement can help tens of millions of users.
I expect Microsoft has lots of telemetry on this....