Drawing more current is easy. Generating enough voltage is a bigger problem.

You can search for functions of portable amps (you can type keywords that are something like that in google).
I'm not an electrical expert, I just know enough to make me able to understand things. 

Basically it's easier for players to dump as much current as the chemical reaction in their batteries allow them to, but when high impedance headphones that need higher voltage to do the same amount of work (loudness) is plugged in, the player alone can't do anything as the battery is limited to a certain voltage.