What if a 'winner' today is a loser in a year? What if we come up with a new approach to solving a problem that requires a breaking change, or a new crate?
Would someone be inclined to try to improve the state of HTTP given a good enough version in std? Would we be ok with discouraging that sort of competitive approach?
To be honest, all I see are downsides to having a huge std lib. The benefit seems to be that there isn't an obvious, de facto choice for what crates to use. But I think that's a problem better solved by crates.io.