Why? Because the headphone output is current limited so you do not blow out your ears using a headset, ear buds, ect.Did you use an amplified speaker? The headphone output cannot drive a speaker directly. Needs to be an amplified speaker.
One would guess that UPMan knows nothing about the earphone jack, even tho it WAS explained.Well, in part that, but mainly that the earphone output only puts out very low wattage (sorry I don't know the number offhand, but likely around 250 mW).