One huge overlooked advantage of using dependencies is knowledge transfer. Software projects (for the moment) require people to write them and people move between jobs. There is a lot of common requirements between different software applications, it would be terrible if everyone just relied on what the standard lib offers.

PS: I assume this would be akin to soviet communism, where the state gives you "everything" and the rest you fashion at home. (being extremely loose here, do forgive me)