Brakes spongy on 97 intrepid

My brakes are spongy on my 97 chrysler intrepid. They are nice and firm
when the vehicle is off, but once its turned on, they get spongy again.

I took it in to get a free brake inspection, and they recommended that I
change the front pads, rotors, the rear cylinders, and bleed the system.
I did all that, and they are still spongy.

Does anyone know what is wrong?

 

Did they at least change the fluid?

 

No, I changed the fluid. I bled the whole system.

 

You did the most effective maintenance.