The more energy in the cell the higher the current it can deliver and maintain its voltage.
As the energy in the cell diminishes, while drawing whatever current, the voltage drops until the cutoff point, at which time discharging stops.
There is still energy in the cell.
If you start discharging again at a lower current, the cell can maintain its voltage for a bit longer.
I discharge each cell at 5amps till cutoff, then 1amp till cutoff.
GTB SS + 13.5 & 10.5