> Who would want to invest in a benchmark fund with arcane(the literal term as opposed to mundane) rules that were privately decided?

There are lots of rules-based funds. S&P is transparently committee based. It’s why dual-class new entrants are banned, but Google and Berkshire are grandfathered in.

There is a genuine debate on rules versus committees in the index world. But S&P has stuck to its guns as a bastion of the latter. And it works. Everyone picking the S&P 500 over its competitors chooses that.