Infect just isn't much of a threat in Commander for the reasons WizardSpartan mentioned. I use it in one deck (Skullbriar) and it's more utility than anything else. I pack both
Triumph of the Hordes and
Tainted Strike in the deck. That deck however is designed to be a 1v1 deck.
Infect just doesn't have enough support to be the "build around" of a multiplayer deck without focusing on proliferate and as WS said, that can be a double edged sword for the one playing it. I did that at one time and it just wasn't fun for me or my playgroup. If there were more effectively costed creatures or ways of giving your team infect, perhaps an overloaded card that somewhat combines
Tainted Strike and Triumph into one with a reasonable cost, then it would be more viable. But without that, it's more of a novelty. With it's ranking on the Storm Scale, it's unlikely either of those ever happen.
And it sucks because I loved infect back in the days.
ETA- I also had a
Saskia the Unyielding infect deck at one point and it just made me a target early in the game.