This is an ideal state, for sure, but it's also where corporate bureaucracy gets in the way. It's FAR easier to have a catch-all, pretty generic posting for a category of role than to get approval for discrete postings for each conceivable instantiation of that role category within a hiring org. This is also why many [tech] companies will include leveling information in the posting in addition to a salary range, so candidates will know that they could be considered whether they slot in as, for example, an IC4 or IC5.