"Batteries included" ecosystems are the only persistent solution to the package manager problem. If your first party tooling contains all the functionality you typically need, it's possible you can be productive with zero 3rd party dependencies. In practice you will tend to have a few, but you won't be vendoring out critical things like HTTP, TCP, JSON, string sanitation, cryptography. These are beacons for attackers…
Frankly inventing a new language is irresponsible these days unless you build on-top of an existing ecosystem because you need to solve all these problems.