Why does "lemon" mean "inferior"? [duplicate]
I think the primary derivation is most likely to be connected with the British slang usage indicated at the etymonline link you've cited: "to hand someone a lemon". The image is of being given something expecting it to be sweet, and then biting into it and finding it to be very sour. You say that the taste of a lemon is never bad, but I wonder; do you really enjoy biting into lemons?