Are Asian Pears Bitter? Mine Was
I think you got a bunk pear.

I've never had a bitter asian pear. The grocery store sign is correct; they are sweeter and juicier than other pears.

Unlike other pears, asian pears are typically picked when ripe. They also are supposed to be quite firm and crisp when ripe. You should be able to smell the sweetness of a ripe asian pear. Maybe your week "ripening" it spoiled it? Not sure what the conditions were, but it is strange because they have an excellent shelf life.