[Nullabillity]

It's more convenient to be able to handle all dependencies through the same package manager.

Personally I prefer Scala and thus use SBT for most dependencies, requiring the user to use Bundler or NPM as well for just one dependency can get a bit annoying. In the case of SBT it actually does have some integration with NPM since it's used so much for client assets (and there is Trireme which is a pure-Java Node clone), but Ruby dependencies still mean adding one or two manual build steps.