Because when the voltage potential or PUSH was reduced the total current through the hunk of resistance (the filament) got lower.
a bulb item is rated for its current, AT the voltage it is also rated at. If you want to know the current of the bulb, you will have to push through the bulbs speced voltage through it too. because it follows the ohms law thing albiet loosly because that type of resistance (filament) changes lots.
as the voltage increases, the current that passes through increases , even if in the case of a filament where the resistance raises some as it heats up.
if you increase the voltage you still increase the number of electrons that try and pass through onto the other side.
(there has to be an easier way to conceptionalise that, and in less words too.)
