That's because she is a blatant expy of Lavos. Her motives are more believable than Sephiroth's, that's for sure.
Garland - FFI
The Emperor - FFII
Cloud of Darkness - FFIII
Zemus/Zeromus - FFIV
Ex-Death - FFV
Kefka - FFVI
Sephiroth - FFVII
Ultimecia - FFVIII
Kuja - FFIX
Sin/Jecht - FFX
Shadow Lord - FFXI
Vayne Solidor - FFXII
Barthandelus - FFXIII
That's because she is a blatant expy of Lavos. Her motives are more believable than Sephiroth's, that's for sure.