When would I ever want to buy Maw of Malmortius?

Since pretty much every bruiser goes + since Sterak's makes the sheen proc stronger, makes you nice and tanky and triggers lifeline off all damage types, why would I ever want to buy / ? I can see rushing hexdrinker into difficult AP matchups but or AP heavy comps but then why would I complete it when I could just buy Sterak's? Maw seems it pales in comparison to Sterak's; • Sure Maw gives a nice magic shield which scales directly off your MR but what about the ADC who is usually not irrelevant • +50 AD is nice but what about my +50% AD increase from Sterak's which will make my sheen proc stronger? • More often than not the enemy team will have reliable Hard CC to pin me down which Sterak's gives me tenacity to help deal with. Maw just gives sustain which how am I supposed to use if I'm CC chained?

I'm just unsure why I would ever want over since it seems too situational and is just so much more useful.

EDIT: I forgot about other classes lol