Why are promos so bad?

I could be playing on a bronze 5 account and I would literally bet money that I would lose the first two games of promos then get back to promos easily then win the promos after. This has happened in silver,gold,platinum,diamond. LOL

Like my teammates have neg win rates and lower mmr yet they are still facing people the same division they are. The matchmaking has 0 logic to it.