Because it's stats are outclassed by other Electric types that fill the same role as it does on a team, notably Jolteon. It's movepool isn't that great either, with it's best choice for an Electric attack being Wild Charge, compared to Jolteon's Thunderbolt (or Thunder, if on a rain team). It can learn a few tricky moves to deal with checks and counters though, such as Ice Punch to deal with Ground types. It's best set-up also involves holding an Air Balloon, which is kinda situational. --- You either eat the world, or the world eats you. Either way, it's okay.
pretty sure he very briefly dominated the 4th gen OU metagame
it was very shortly before I stepped into it, put one in my team, and got laughed at horribly for it because my team was entirely ruined solely by the inclusion of Electivire, which turned me off "rate my team" threads forever --- 4639-9811-6534 -Pokemon X/Y Friend Code. PM if you add. Trainer name: Marii Friend Safari: Grumpig, Sigilyph, Girafarig
His movepool is what got me interested, he can have ice punch, wild charge, earthquake and flamethrower. That's a pretty damn varied movepool and he has a high attack stat & speed to get rid of some threats quickly and effectively. But then again I haven't got to test this out myself so...