The problem is that the ruby versions packaged in the distros are not always as compatible as one could wish.
Sometimes it is the list of default gems that is different (like how fedora packages bignum as a gem), and sometimes it is the distro packaged gems that just doesn't look like the stock versions. I've seen examples of gems split into two gems, as well as gems that has had their version dependencies altered. things like that easily makes either rubygems or bundler very unhappy.
The thing about distro packaged software is that you have to trust the distro to do the right thing, and it only takes so many examples of them doing something stupid before that trust is lost.
Sometimes it is the list of default gems that is different (like how fedora packages bignum as a gem), and sometimes it is the distro packaged gems that just doesn't look like the stock versions. I've seen examples of gems split into two gems, as well as gems that has had their version dependencies altered. things like that easily makes either rubygems or bundler very unhappy.
The thing about distro packaged software is that you have to trust the distro to do the right thing, and it only takes so many examples of them doing something stupid before that trust is lost.