He missed my most crucial requirement: Can a package manager support more than it's chosen language? Am I forever consigned to vendor lock-in?

Every one of these tools is 100% focused on supporting a single language. They go so far as to use that language as the build spec so even attempting to bend it to another platform feels alien. It's okay if I only ever want to use Ruby or Javascript will be my thing for the next decade. But what if I want to take my existing npm or gem workflow or knowledge and apply it to a new language? I have to start all over from scratch. I'll have no idea how to fetch dependencies or package up my stuff for sharing.

If I start to tinker with more than a handful of languages, my head is going to be full of details on package management rather than APIs or library capabilities. Who wants that?