The only problem I see with Wormarg's is that it is situational. It was designed to give high health champs (who didn't scale well otherwise with sustain items) a means to top off their health and rejoin the battle, without having to return to the fountain.
And wormarg's is good at what it does, but how useful is that really in the thicket of a match? For a tank or Juggernaut, chances are you want more suitability in combat, rather than out of combat sustain. (Unless say you were on ARAM where you couldn't recall) The only reason Tanks would need that out of combat sustain is to counter a poke comp. (also common in ARAM)
It's not popular, it's not meta, but it is good at what it does.