Moat is just goddamn aweful in UW Landstill. Your factories/Elspeth tokens can no longer attack, and it doesn't stop one of the more difficult threats to get rid of i.e. Tombstalker. Moat does help Elspeth's second ability, but the limitation is not something good to have, especially in a deck that needs to have answers from many areas. Attacking with ONE flying Factory while the rest sit at home isn't that great. Landstill is perhaps more fearful of Tombstalker than Dreadnought/Goyf since our other removal EE cannot get rid of it. We have Spell Snare/EE/StP against Goyf, so although Moat stops that, it doesn't stop Tombstalker.

Not to mention that Moat dies to Qasali Pridemage which is popular in Zoo and in UGw Thresh. Humility shuts down ANY CiP abilities. Moat doesn't stop Imperial Painter from fecthing Servant and win, but Humility outright wins those matches and it has MUCH more synergy with Factories and Elspeth whereas Moat kills those cards. Since the printing of Qasali Pridemage, I think the incentive to run Moat has decreased unless you're running Exalted Angel in Stax, but you recently see more white Stax utilizing Elspeth as win condition since Exalted also dies to many of the removal in the format.