I think it's safe to say that the programmers created the bracket-style tournament within the structure of the existing tournament architecture. Multi-round tournaments already require that you set a time frame for each round. Bracket tourneys are in essence, multi-round tournaments.
I would further venture to say that changing the multi-round time frame logic may not be as easy as it sounds. I would also bet that they had already thought of this and decided it was best to leave that logic alone for now and move on to other improvements. Nothing is broken. Nothing is unusable. Leave it for another project.
It's a great idea and seems logical, but I wouldn't blame the developers for not doing it because they just don't want to listen to their customers. I'm sure it's a lot more complex than any of us know.