They've acknowledged that AD Ezreal's W is lackluster multiple times in the past. Meddler commented on this the last time they buffed him, when he was asked why they buffed the E instead fo the W. The answer was that redesigning the W into a more meaningful skill (not just more damaging) for him would take up a lot of his power budget and would require reworking his other abilities to some degree, which doesn't seem like a great idea to rush into because he's preforming well and is a very unique champion even without having a good W.
At some point in the future they want to address it, but it's low priority because he's preforming fine and people are generally very happy with Ezreal right now. It's just too hard of a fix for too little potential reward, which gets it shelved for now.