Waivers are not a cookie-cutter process. Each is manually evaluated by FCC staffers, many of whom are JDs, and may be accepted, accepted in part, conditionally accepted pending more information (like the East-West Gateway waiver request), or dismissed. No guarantees. They are all different and offer different reasons for asking.
The biggest problem has been that licensees migrate to another band and still find a reason to hoard their lower frequencies. A regional planning committee has no authority to make them cancel their lower frequency liceses (effectively giving them back). So this played a part in the St. Louis region showing public benefit.
The other thing to note with STL is that EWG is NOT a licensee (they had a license for their MEDCOMM program, which they unbolted and disassembled when grants funding for it ran out; it was dubious whether they qualified as a 90.20 eligible entity when they got it). The FCC is requiring each entity claiming this waiver to write in and let them know exactly which licenses are relevant, what they intend to give back, and what they intend to keep (ostensibly common channels for mutual aid... and nothing more). So this comes with strings attached.