Two possible reasons for not using ENLP:
One if you move to a Windows computer or want to share your library with a Windows user the Windows machine cannot open an ENLP file it is a MAC specific format that only works on a MAC.
You would need to compress and send an ENLX is the best way to share or move a library to another machine.
Two is that if your library ends up getting damaged and needs to be recovered, you cannot directly recover an ENLP library you have to remove the library from the package file before you can recover it.