Liandry's Torment Discussion in Pro Play

It seems that LIandry's is being built almost at random by ap mid laners in LCS and I'm not understanding why. Often it is built when the enemy team has 1 or no tanks, and if it was meant to be a defensive option, zhonias is usually a better option for most, while rylias for the rest. Can someone explain or link to an explanation please?
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