Because you probably still have your handbrake on.
If not, than you need to see the car-doctor.
it has a sticky handbrake switch
If the handbrake is not engaged, and the warning light is coming on, it may mean that there are components in the braking system that require maintanence. Or, it could mean that the master cylinder is low on brake fluid.
The handbrake light is also the 'low fluid' warning light. It is connected to the handbrake as that ensures that it is checked every time you use the handbrake. If it remains on all the time, then check the brake fluid and top up if required. If the fluid is ok then it is probably the switch on the lever and is adjustable.
Typically this bulb serves 2 purposes: 1) low hydraulic level in braking system reservoir or 2) faulty handbrake switch (handbrake still on) Pls check them both and feedback.
it means your handbrake is on
usually a sticky switch on handbrake, had any welding recently ?, worn shoes ?
your switch that tells the car that the brake is off is defective
I have the same thing with my 220Gsi.. It seems it has nothing to do with the handbrake though. I suspect it has to do with the level of your steering fluid. I will check it out and let you know later this week
Release the handbrake
Either your handbrake switch is broken and will not turn off or you have low brake fluid.
Either the switch (on the handbrake) is sticking or you have a short circuit, usually caused by corroded wires or connections.