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.

It makes sense for multiple job ads if there are completely different roles applied by completely different people. But, for the sake of hiring, it doesn't make sense to invent new titles just to justify differently negotiated salaries. For example, I was once hired as a "Senior Software Developer" who essentially got paid twice what the least senior Senior got; they were to some extent mislabelled: They were senior in another capacity than software, and had transitioned inside the company but kept their titel because people are vain. Our responsibilities were vastly different: He was a frontend tokenmaxxer, and I migrated strategic customers to on-prem Kubernetes by negotiating contracts, bootstrapping clusters, and adapting applications to run without autoscaling. They could have given either of us a different title, but for the sake of the value we added, the salary made sense.

A title like "Senior Software Developer" can range from 5 years of general-purpose web development experience to 20 years of highly specialized experience. Those "Principal" and "Staff" titles don't necessarily make sense outside of larger corporations.

Most recently I've seen salary ranges up to 30% of the upper bound. Completely reasonable.