As I explained before, it is Yet Another Source™ for installing things from. Creates an additional headache: "Where does developer X put updates to patches Y and Z?" Instead of a single source, I now need a matrix. I am a simple man, I like keeping things simple.

It is the same reason I still use Skype, for example. It was the first IM system I started using 15 years ago and never has the need to switch to anything else. It still performs the same functionality it did then, so where is any compelling need to switch?

To each his own. Some people change communication tools, clothes, cars, gadgets etc with fashion. I change them when I absolutely have to.

EDIT
To cut it short, I do not have anything against PM2. It's just that I never saw a reason for using it.