I would say that relatively few accidents are survivable, and of those, not all would allow time for correct donning of lifejackets and evacuation. Even if that happens, it does not guarantee survival.
Thus we have to place a value on human life versus the cost of carrying, supplying, and maintaining the lifejackets. That's impossible, and for that reason I suspect that most airlines, and certainly those operating over or close to water, will continue with lifejackets, however pointless they might seem.