I notice that nested team must always inherit their parent team's timeline. What is the rationale behind this decision?

I ask because some larger projects structure their teams by skill and nested teams will be on different timelines. In the example teams below, Operating Env and Application have differnet schedules.

-Systems
-Program Mgmt
-Software
-----Operating Env
-----Application

A solution would push the OE and App teams to the root so they could have their own timelines. But then we loose the ability to roll-up progress for all Software teams and the RTC teams don't match our real organization. Thoughts?