I do not have projectile installed, but since Emacs 25.1, Emacs ships with a built-in project.el library and I use that instead.
I made this the fall back option because if a user went to the trouble of installing a 3rd party library (projectile), he/she probably prefers it over the built-in solution.
I did not think it would make sense to have project.el look for a project root if projectile is installed but did not find a project root.
I do not have projectile installed, but since Emacs 25.1, Emacs ships with a built-in project.el library and I use that instead.
I made this the fall back option because if a user went to the trouble of installing a 3rd party library (projectile), he/she probably prefers it over the built-in solution.
I did not think it would make sense to have project.el look for a project root if projectile is installed but did not find a project root.