One thing to realize is that a manager has a lot of things to consider for their job in totality. Hiring, planning, documenting, budgeting, retention, lateral and upward management, team stability, etc. I'm not suggesting to be apologetic to them, but at most places, a manager has to put up a bit of a fight to get a significant raise for a subordinate. Even more so if it's out of salary band. Even more so if it's out of cycle. Most managers know their budget of political capital, and know the abstract cost on getting someone a raise out of thin air, and many feel it's squandering.

If a manager is just plainly average at their job, then they'll probably prioritize what is very clearly and evidently an issue/task for them to do, which is usually what their boss is asking them to do, for better or for worse.

So it's not that a manager is being deeply unethical and withholding promotion potential because they're evil, they just may not see it as a priority among everything else they have to do, especially if the subordinate in question appears happy and fulfilled.

I agree with some others here. To really ensure you're being paid fairly as an employee, you do have to normalize making it a discussion with your boss. If it's a priority for you, it'll more likely be a priority for them, assuming they look at you in favorable light.

I wouldn't blame anyone personally, but it is what it is. If eventually, this is what's happening often, then the workplace feels unjust to me. It doesn't matter if the cause is some manager, HR, CEO, etc.,. (Sometimes I imagine it can even be the cultural impact of somebody that already left the company...)