Spell vamp in general was seen as an un-healthy stat but was only abused by two champions, where as 
and 
aren't seen as un-healthy to the point of warranting removal. Then there is life steal oh boy, If anything I think riot should have just gimped the two abusing it by making spell vamp like 30% as effective on them given their innate healing but the item previously made for some wacky builds.
There was two main reasons
If it was balanced on everyone else, it was BUSTED on Vlad, and if it was balanced for Vlad, it was garbage for everyone else. No amount of nerfs really changed that either.
Mages tend to want to get in, blow all their cooldowns, and get out. That makes the healing rather mediocre because you either picked a good time, got everything off and got out, or you got CC'd and died, and the spellvamp meant nothing. Mages would rather have more AP from other items so they kill them first rotation instead of having to go back a second time and healing a bit. In contrast, look at how ADCs function. They want to consistently attack and do damage so the healing is super relevant to that because they're in range of the enemy.
I do wish it came back, i always prefered it over gunblade on Mordekaiser.
Id love to do Will of the Ancients, Protobelt, Lichbane, Rylais, Liandries, Lucidity boots on Mordekaiser again :c
WotA was only unhealthy on certain champions (namely 
). The rest of the time, it was a trash item and a nub trap.
Most mages don't benefit from spellvamp as they are usually AoE burst-type and due to WotA's AoE limitation (5% only), they wouldn't gain that much hp anyways once they unloaded all their spells.
WotA was only beneficial for DPS/poke mages, but WotA's stats didn't benefit those types too much (due to their need for CDR and mana). Only one that really worked was Vlad (and maybe Cass, if she got her Tear stacked well).
Perhaps instead of it giving back health, spellvamp could be a form of 'mana drain', where X% of the damage is taken from the enemy's mana pool to be given to the caster instead.
ADC's lifesteal deals with health, so it would make sense that Mages' spellvamp dealt with mana.
It was most likely because the item was FAR too niche to the point it was really only effective/worth it on one champion.
