You can use the instructions here:
To convert this bundle:
Is there any concrete reason NOT to include the highlighting in pre-made package?
The amount of features that the core team can support by themselves is finite.
As a modular editor, Atom benefits from having a slim profile of core packages. There’s less room for introducing new bugs into the core when the functionality of the core is limited, and it keeps the development team less stressed. On the user side, it’s easier to build your own Atom if you don’t have a whole lot of built-in packages that you need to disable because you aren’t going to use them. It’s possible to distribute whole suites of features, and there are a number of packages that are more broadly applicable than EJS that don’t make the cut because the cut is deliberately erring on the side of being minimalist.