User blog comment:RoznosicielCiast/Least popular champions/@comment-5185239-20130125022429

Karma isnt played because her support ablilities are horrible compared to other support (her lvl6 heal having worse base values than sorakas lvl2 heal; her shield being just a plain shield without a secondary bonus, unlike Jannas or Lulus; her lack of hard CC (well, of any form of CC tbh) makes her no threat in fights; etc.).

There are reasons people don't pick Karma, it's not because people don't know how to play them (1 cone ability + 2 targetted spells + ult on activation ain't that hard), it's because they dont offer anything to a team. Why would you need a champion which offers a (situational!) slow, when most of the mid laners have a stun, taunt, silence and what not.

Her clear power is early on strong, but after six champs like Anivia can easily push against her. Her heal is weak in comparsion with other supports.

Also:

-6 levels for every skill = more effectiveness - No...

-Hard to understand skillset - A cone which deals damage and can heal, a leash that speeds up allies and slows enemies, a shield which can deal AoE damage around stuff, not very hard

tl,dr:

Karma is useless for nearly every comp as there is always a better choice for the support or    mid lane. Her lack of CC and damage late game make her a one-trick-pony early game and thats about it.

Please stop thinking that it's actually the difficulty or secret OPness of a champ which makes him so unpopular when it's obviously lack in his kit and the difficulty of fitting in compositions or the actual meta.