What can be causing low spongy brake pedal?

Just had front rotors replaced break pedal still feels spongy ....it stops and has pressure to it but my pedal is going down a little too far( when car comes to a complete stop my free foot just barely fits underneath pedal, and pedal comes back up with no problem) did a master cylinder test to see if when brakes are pressed if there was any bubbles in reservoir and there wasn't any, I'm not losing any fluid so what else can it be ? I have a 97 lumina with ABS....brake lines are new as well as a caliper(driver side)