Maybe you're thinking like Facebook, but AIUI, login with Facebook is proprietary. The problem there isn't the protocol, it's that companies are massive. If anything OIDC lowers the barrier to entry, assuming RPs properly support it (which is a huge if, but if these were 3 proprietary protocols instead of 1 standard one, there would have never been a chance…)
Maybe you're thinking like Facebook, but AIUI, login with Facebook is proprietary. The problem there isn't the protocol, it's that companies are massive. If anything OIDC lowers the barrier to entry, assuming RPs properly support it (which is a huge if, but if these were 3 proprietary protocols instead of 1 standard one, there would have never been a chance…)