In a node process you can't run 2 things at the same time without forking an external process. That's why these libraries exist. A complex synchronous computation will block the only thread available in nodejs. Sure you can spawn workers, but your node workers will have the exact same issue.

> all reinvent the concept of threading poorly

because "user scripts" in node have no concept of threading to begin with. There is no concurrency in a node process, only non blocking I/O.