Node NPM rocks 15 years ago
The problem with rip is the lack of cross platform support due it's usage of symlinks.
Its management and mixture of git/gems can make things a bit complicated.
Not to mention that it plays with your environment variables (RUBYLIB) making things not as transparent as npm.
Node really endorsed npm and both worked together. RubyGems until 1.9.1 was never part of "Ruby", even while is extensively used as package manager.
Worse than that, Ruby-Core doesn't use it and cripples it to avoid the startup pain it could be, instead of making it integral part of Ruby.