Originally used activationCommands but this prevented styles being loaded automatically from styles/ directory (?!).

From @Aerijo in Slack (preserving here because, well, Slack ain't forever):

@xurizaemon It’s the activationCommands entry in the package.json that is messing with it. I suggest removing it, or separating the package into a standalone grammar and whatever the lib files were meant to do. Personally, I believe packages should be as modular as possible.
activationCommands are just a way to lazy load your package. E.g., if the user never uses the package commands in a session, it never needs to load the package.
(Obviously that laziness affected style sheets too).
Overall though, it’s a nice feature to have; as Atom can be used for a wide variety of languages, this allows only necessary packages to be active in any given session. A better hook (that should work) might be atom-wrms:grammar-used, which activates the package when the grammar is used in a file.