It could be a few things: it could be that it’s an incredible item, BUT Azir needs mana, attack speed, AP and penetration more because of how his kit works.

This is a case where it isn’t a bad item, it’s just others are possibly needed whereas Liandries is only a “necessary” item on champs with dots or low cooldown poke - Malzahar comes to mind.

He likes AP and mana and CDR, but he also likes HP because of his short range and when you see his kit you find he gets a little mana back from his E. One of his main spells is a dot, and he has two ways to enhance the burn on the item, so it just fits him great. He’s also not really a burst mage, so the ramping damage aura works nicely on him.

Contrast with LeBlanc - she’s short ranged too, so she would like HP. BUT - she has no mana regen, she can reposition herself (technically up to 4 times) and she is actually a burst mage. Liandries doesn’t suit her as well, even though she doesn’t hate the HP and AP and extra burn damage is extra damage. But Morello works better for her because it grants penetration which syncs up w her play style better.

So it’s not that it’s “bad” - I think most would agree the item is excellent just on it’s own but you’ve got 5 slots plus boots in most games, and many champs have items that synergize better is all.