During a fire, why do firefighters wait until everyone is out of the building before attempting to extinguish the flames?

Smoke kills people most time an extinguished fire still has smoke for a time. And the PSI in a fire hose can be regulated while they get people out of the building but too low of a pressure will create a situation where there is not enough water to extinguish the fire; too high a pressure can possibly injure the fire crews inside the building.
http://www.fireengineering.com/articles/print/volume-165/issue-10/features/every-pump-operators-basic-equation.html