Eelektross is a classic case of Jack of All Most Trades, master of none, much to its detriment. Which is a shame cause there is a lot of good going for it. Balanced Offensive stats and a wide movepool with coverage options most Electric types would kill for is a great start. Levitate is a good ability, providing Eelektross no weaknesses and immunity to most entry hazards without being weak to Stealth Rock, which does compliment its above average HP and average defenses.
However for every good thing on Eelektross, there is also a bad. Lack of physical STAB outside of Wild Charge hurts a lot, especially when Eelektross is reliant on its bulk. And Special sets, despite having many valuable moves, are running off a lower Special Attack that Eelektross has no way of boosting. And while a lack of weaknesses is nice on Eelektross, there is also a lack of resistances, which is just as, if not even more important, as resistances and immunities are enables a Pokémon to take hits. Recovery being limited to non-STAB draining moves hurts as well, compromising Eelektross' ability to take repeated hits. And it all comes back to Eelektross' poor speed. Thanks to that horrid speed, offensive sets struggle to apply pressure. Thanks to that horrid speed Eelektross must take attacks before retaliating or recovering, ruining its decent bulk. Eelektross' speed makes all of Eelektross's flaws worse.
And in the end, while versatility is good on a Pokémon, optimization is also important. Being decent at everything means little when your competition excels at one particular role and can have teammates reasonably pick up the slack. Eelektross' flaws require excessive support in more inclusive formats, which just leaves passed over for many better picks.