It's a matter of the brushes not generating enough force to cause a loose drumhead to vibrate a whole lot. In jazz contexts where I play a lot of brushes, I most certainly do tune higher.
Or I would word it like this ... that there's not enough weight and force coming from the brush to move the air inside the drum once it strikes the drumhead.
Jazz drum tunings are typically higher for all the reasons mentioned. Dynamic range, controlled sound, reaction time, etc. If the Tom head is tight, it takes less effort to get a full sound from the drum. You can tap the drum and get a full sound. If the drumhead were loose on the Tom, you'd have to lay into it more, more energy to move the skin to excite the air inside the drum to create the full sound. The air has to move enough to excite the resonant head ... if you want the full sound from a double-headed drum.
The lower the tuning, the slower the vibration and air movement.
