Hello, just my 2 cents here:
I can remember a forum post where it sais, that Liandrys is getting procced by morellos debuff. So if you wanna take Liandrys later you will get a good amount of damage on top for morellos since some more seconds of proc can be a big amount of hp. Especcially on champs with good poke. Dont know if its really true or if Liandrys is bought that often in LCS, because i rarely watch a game, but it could be an explanation. Sry for missspelling. I am not an natural english speaker