Earlier quoted context omitted.
I think he means stuck financially, not career wise since they have chosen to stay as a developer. His answer to how to move ahead financially is to specialize. So maybe that is the general advice is to find something to specialize in or you are just seen as a commodity by management. If you are a commodity (e.g. general web developer with X years) then you may not get higher rates.
I agree with the general idea. You can remain a "simple" developer and still ask for more money if you specialize and bring significant value. I disagree with the idea that moving to a management position means that you get "unstuck", especially financially. To me, becoming a manager is pivoting or branching out, not specializing. And as I stated, a manager should not necessarily make more money than the people they…
Depending on the level of management and the systems involved it could also become involved in audits, regulatory matters and potentially handling confidential information for the company. Think of it this way: a manager of a team of 10 developers probably has a budget of 1.5 - 2.0 million dollars in just headcount, maybe higher. If your average developer on that team makes $100k, isn't it worth it to have the manager make about 20% more because of the responsibilities?