Rodgers used Allen because he wanted to keep possession. Without Suarez in the team we're not kamikaze and there's a lot more controlled build up with emphasis on trying one-twos and team moves in tight spaces. City defended well, especially Dimichelis, and we struggled to get through their wall. I don't think our team is technically good enough to tear through teams in that manner yet. We got a couple of half chances but nothing more really in the first half. Still comfortably the better team, and we really did play well. We weren't causing them too many problems but if we'd scored one, nobody would have said it was unfair. And Allen was a part of this, he kept the ball reasonably well and always offers an option. Never gives you penetration, but very good for keeping possession and just recycling it.
The problem with him is that when you go a goal down, you need attacking threat in your team, and Allen doesn't offer this even remotely. He's about as useless a counter-attack player as you can get and too often he slowed our attacks down, refused to play a riskier pass and just kept hold of the ball and played it backwards. I don't blame him, because playing risky passes is not his game, and he regularly flops at even slightly lower percentage passes, but he's not the player we need at all when looking to chase a game like against City. He was poor second half and we need an upgrade I think