Soft Brake Pedal

I have a 2006 Pontiac GTO. When I bought the car (new) it had great brakes. The brakes started working as soon as you touched the pedal and were linear. By 25000 miles the car would still stop but the top half of the pedal travel isn’t really doing much. I had the rotors turned and new ceramic pads installed as the old ones were cracked. My brakes feel the same. Thinking there may be air in the lines, I had them bled and all the old fluid cycled out but the pedal feels the same. I’ve heard that the type of rotor/pad you use can cause this problem but I don’t understand how that can be. I appreciate any help anyone can provide on this

Make sure you rear brakes are adjusted, back up and brake hard a few times to set the self adjusters. Does the pedal hold when you are stopped? If it continues to move check for leaks.

I would think this kind of car has disks in the rear, so no adjustment.
Could be a bad master cylinder,but it’s premature.
Could be a bad part in the ABS system.
Could be a damaged rubber hose that swells.