This is true, but a good manager is worth more than many engineers.
These engineers can be a huge factor in the success of a project. I'm not saying good general managers aren't valuable, or that they're easy to find, but they're a bit more of a commodity. They aren't those extremely rare birds like highly talented engineers who can coordinate the efforts of a team and bring a highly complicated project through.
Unfortunately, I think we sort of miss this in our field. Top lawyers and physicians continue to call themselves lawyers and physicians, even as they rise into "management." They may hire "managers" at their firms, but true leadership in a complicated legal case, for instance, requires a very senior person who is so deeply immersed in the law that it makes more sense to call him or her a lawyer than a "manager".
In short, nobody thinks that a person decided not to "go into management" because his or her title is still Lawyer, or Surgeon. We seem to place a stronger dividing line in engineering.
You know, that may be (yet another) reason young people with options don't go into software development or engineering. Maybe they don't like the end game, and prefer other fields for that reason.
To achieve anything hard you'll need a team of engineers. That single good manager is going to be the one that attracts and retains those good engineers. You need few good managers but they're much harder to find.