Good question ..
.
Sign on a traffic pole:

Been waiting long?
That's because the council thinks someone in a car, half a kilometer away, is more important than you*.
They could make the lights change as soon as you press the button if they wanted, but they don't.
Complain to them 07 3403 4400.
A car moving at 50km/hr will travel almost half a kilometer in 30 seconds.

@RustyFreewheel FWIW I've noticed wide variation between cities in how friendly traffic lights are to pedestrians. Melbourne is fantastic - the lights usually change within 30 seconds. Perth is probably close to the opposite extreme, where it's usually quicker to just cross when there's a gap in the traffic.