A few reasons we don't just use submodules - The Go community supports Git, Svn, Bzr, and Hg. We keep that up. According to the Eclipse community survey, 2014

A few reasons we don't just use submodules - The Go community supports Git, Svn, Bzr, and Hg. We keep that up. According to the Eclipse community survey, 2014 was the year Git usage passed Svn usage. Svn usage is still quite high. - A lot of developers struggle with and even have strong negative opinions of submodules. So much so that we now have subtrees. I've find a lot of developers would prefer not to use them. - The way Glide works is in line with the package managers from the other major/popular languages. This way it's familiar to many people coming to Go by solving the same problem in the same way they're already used to.