I have seen the bellcranks frozen and the cable seized which will not let the adjuster auto adjust the rear brake shoes. If this happens or you don't ever backup using your e brake on occasion The shoes continue to slowly wear down increasing your pedal travel because the wheel cylinders have to more fluid to move to apply the brakes in the drums.

Before, I fixed my emergency brake properly, I would check my rear drums ( every 5K miles ) to make sure they slightly dragged. If they didn't I would manually adjust the brake adjuster to keep my pedal decent.

Now if you are sitting at a stoplight with your foot on the brake pedal stopped. With you feeling the pedal creeping to the floor slowly moving. Mostly that is caused by seeping o rings on your master cylinder plunger itself.