Leona is my choice when I feel like playing a murderous tank... So a little while ago, I started trying her in the jungle because, if Amumu and Sejuani can do it, why not Leona? So after a game where I did exceptionally well, it made me wonder, why don't people play Leona in the jungle?
Faie6 votesHer clears are lackluster. She doesn't have enough damage to kill the jungle creeps because so much of her damage is locked into her passive. Also, her ganks before 6 are weak. She has to use her entire kit to engage a gank, which means that if she gets counterganked, she'll be useless in that situation. She also cannot 1v1 well, so she can't counterjungle and defend against counterjungling.
Mostly though, it's because her damage comes from her passive, which she cannot herself activate.
Nivloc1 votesYeah. That passive damage.
what you deserve3 votesHer ganks just aren't really as strong imo.
Elindiir1 votesOk, I will admit, Leona needs a bit of laner cooperation... She can't flat out kill people unless they are pushed in and squishy...
what you deserve1 votesIf you're in a premade 5, you can do things like that because you have better communication, but for soloq you just kind of need to either straight up kill everything or totally spoonfeed all the kills. That's why Rengar and Fizz can work in low elo jg even though they're not really good- they're just super strong assassins.
Baby Ghoul2 votesWhy not get you one that can do top, jungle, and support? 
Seriously though I'd be down for a solo lane Leona. She's not built for that right now though. People have been asking that for a long time, but not in the jungle, in top lane where other tank/supports go. Her ganks would be okay, but her clear time in the jungle would be painful. Clear time matters so much more than ganks right now.
Amumu would be very bad for support. Many people think you can make any champion into a support, but in reality they need to be able to do a lot with a very little. Amumu can't accomplish much early game and other champions offer better utility and effective early games.
1st Movement1 votesjust roam as leona support
amumu needs a lot of mana in order to be useful and items which he cannot offer as a support leo has bad jungle clear ,
your off better using gragas , strong clear , tank and mobile
Fondling Gems1 votesLong time no see :P
As stated before Leo jg has waveclear issues although I personally think her ganks aren't that bad. Amumu sup has the issue of lacking cc pre 6 and lanes are often decided pre 6
Support Evelynn1 votesJungle Leona is fine. Just get bami's cinder or a tiamat asap and your clears will be great. Her ganks are bar none one of the best in the game, S+ tier for sure.
Paladin 0f Life1 votesThey used to but riot didnt want it to happen and amumu sup is viable if played right.