Given their huge variety, why is it so often concluded that the penalties needed to use a Weapon of Legacy are never worth it?

A common trend when discussing Weapons of Legacy is to compare their benefits to that of normal magical items, notice that they pretty much match up, and then conclude that because the Weapons of Legacy have extra penalties associated with them, they are clearly inferior to any comparable normal magical item. However, some of the benefits of some of the Weapons of Legacy are as good as unique (for there level, at least), so how is it so frequently and easily concluded that their extra penalties outweigh their unique benefits? What I’ve just linked does a fairly good job of assessing the value and rarity of said benefits, but despite the frequency with which I’ve seen the claim that the penalties for Weapons of Legacy always outweigh their benefits, I’ve never seen any such analysis of their penalties, which are rather varied. What property of these penalties is so severe that it allows the Weapons of Legacy to be disregarded without any further analysis, despite the variety in these penalties?