[LukasMathis]

The examples you mention (e.g. programming, then looking something up in documentation) only require you to switch between apps rarely. In those cases, it makes sense to let each app take up the whole screen. The additional screen space each app gets is worth more to you than the mental cost of having to switch between screens.

In other cases (e.g. writing a cover letter or a job application while looking up information about the company on their website), you constantly refer to two different apps, so it makes sense to allow both to exist on the same screen.

There are valid use cases for both behaviors.