ABC was originally designed for European folk music [0], not church music. The corpora as a result is largely fiddle tunes, particularly Irish (see for example https://thesession.org).
ABC started very simple, because most of the performance information for folk music isn't written down, it's inferred by the player according to the idiom of that particular tradition. As usage of ABC has grown it's gotten more powerful but still falls far short of formats designed for western classical, like MusicXML or Lilypond.