The same developer who worked on bundler also worked on the initial version of cargo. That’s why they’re similar.
And at that time, it was a good idea. Ruby was popular and bundler + gem ecosystem was a big reason for its popularity. No one was worried that Rust might become so popular that it might outgrow the bundler model. That was only a remote possibility to begin with.
A mistake that many programmers make, as if baking one more feature on top would have made any difference that wouldn't be amortized in just a few weeks... Sigh.
And at that time, it was a good idea. Ruby was popular and bundler + gem ecosystem was a big reason for its popularity. No one was worried that Rust might become so popular that it might outgrow the bundler model. That was only a remote possibility to begin with.