Don’t mix up the two. Composing and notating are different skills.
I think most people – even most musicians – confuse the two. I know many songwriters who wouldn’t call themselves composers, even though that’s what they are; in their head, composers are writing notation with a quill pen on parchment, or something. For them, composition=notation. But the composition happens independent of the notation – notation is just a representation of the music, not the music itself.
While notation is important, and a skill worth mastering, it’s not composition. And composition need not require notation. In fact, guiding a kid through an assignment to “compose a short piece” I advised him that using Garageband, an phone Voice Memo, or any other way of documenting the composition is acceptable. Composition does not require notation.
Further, I think that the demands of excellent notation skills, and there are many, scare many people away from composing. Not feeling confident in Aural Skills classes, or not growing up with notation, can lead many a young musician to think that they can’t compose because they can’t notate. And then their voices are silenced.
Many of the greatest compositions of the last 100 years weren’t ever notated until someone asked to buy the sheet music. From Louis Armstrong to the Beatles to Jacob Collier, the music came to life through the performing, and only later was there a notated form created to represent the music.