1) because it was never standardsised in the protocol so apps did their own thing.
2) in an attempt to make creating a simple client easier so it doesn't need so much custom rendering.
Discussion
1) I know of no app that does render any of this in compact renderings (quoted events, one liners, ...)
2) that leads to barely anyone building libraries for the hard stuff, that can make building the beautiful experiences, that people actually want, easier
Much more thought went into ATProto lexicons, have to say.