SE Editor-in-Chief here. We selected the William Cullen Bryant translation because we felt that, of the public domain translations, it was the one most accessible to modern readers. We also host his translation of the Iliad.

Pope's is certainly very beautiful, but also very literary and written in a style of English that can be difficult for the average modern reader. I think that determination is well reflected in this survey. Maybe we'll do it too one day (our current collections policy declines alternate translations) - it's certainly deserving.