This may be one factor but it’s not the only factor. “Certain players letting the team down” isn’t something I fully subscribe to as an isolating factor either as Ultra banned Polar, Pein and Orca from his game and scum still won.
This would create a ton of WIFOM and spec. Plus a lot of problems over where the line on “transparency” is drawn.
People can decide whether they think someone is a good host or not and choose to sign up based on that. If they think the host is too inexperienced or a loose cannon, they can suggest a co-host or wait until a host of their choosing plays.