Is there any reason people don't run 
on Mage Supports, like 
or 
? I've noticed most pros don't even finish building their support item, just sitting on a 
instead of finishing it into a 
until much later into the game. I can't really see a reason would be bad as Support, the Grievous Wounds would put in work to negate the enemy ADC's 
, and both the CDR and Mana would help throughout all of the game.
Lemme know your thoughts [slayer-jinx-catface]
Personally, I don't build it because Sightstone and boots are higher priority to me. By then, the mana return on level up from lost chapter is no longer needed, and typically I want a more hybrid defensive/offensive item so I don't go instantly splat when someone looks at me funny. I mean, I'm already behind on gold and levels, I need something to give me a little more defense.
Whilst Morello's has the potential to be effective on a support, here are some likely reasons why it isn't used:
is purely an offensive item; supports might forego it for an item with defensive stats because it is pretty risky for a mage support to remain squishy in the mid game or 
so it's dependent on getting kills in lane
)I think the only situation that Morellonomicon would be viable in is as an offensive, kill-dependent lane that aims to get ahead and snowball. It does not work if the lane falls behind or the supp intends to roam a lot.
supports are supposed to be supports.
they get very little gold so that should be spent towards something that helps your team. not yourself.
Nomicon is not only expensive for a support but it only benefits them other than the grievous wounds which is very low value since its situational.
supports can build hybrid ap items that are cheaper just bring more value to the entire team.
sighstone is necessary, banner of command for ap is ok, zekes has some ap, athenes, ardent censer.
all of them have ap and help your team in some way and are generally besides banner cheaper.
no reason to sit on spellthief, but sitting on frostfang is pretty efficient but if you're not going to get frost queen until late, get the eye
but as for why I don't get morellonomicon... because it's mostly just a bunch of AP. There are much cheaper options for cdr (like eye of the watchers and kindlegem)
I usually take executioner's calling before I take morello as a support. If I need grievous wounds I want it to be up all the time, not once we get the enemy's health down to 35%. If he's healing from lifesteal/abilities, he's likely been doing it for the other 65% of his health too.
Supports get more cdr than they know what to do with, and I don't usually get to build enough AP before the game ends to really matter in that aspect. Rather use the extra 1500g for something else.
I used to build it, but now it's easy enough to hit the cdr cap with other support items (ardent censer/lucidty boots [which are useful for the summoner cd]/locket/zekes), and theres enough mana regen on those items too to cover most support needs.
Morellos grevious wounds can sometimes be useful if they have a heal heavy team, but really your adc should build executioners in that case for the application on every hit, compared to the sup (with morellos) only applying it when they're below 30%.
It's pretty expensive, gives CDR (which supports get enough of), and gives mana restore which supports also do not need.
Dunno why they don't finish earlier tho
Two reasons. First, there are generally other more important options which bring team utility. For anyone except the most damage-focused of supports, helping your team is more important. Second, even if you are damage focused, it's still not cost-efficient. Support builds can already incorporate enough mana and mana regen that they don't need the item, particularly since supports spend less mana in the midgame due to not farming waves as much as a mid mage would. Morello's isn't cost efficient enough on AP and CDR alone to make it worthwhile, and grievous wounds is very rarely going to provide enough value to make up for that.
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