Pontryagin is not simply an elite theoretical mind. On the contray, he illustrates in person the many aspects of the problem. During the fifties, he virtually vanished from public and came back years later with a Lenin prize and "The Mathematical Theory of Optimal Processes". Examples in there include 'two flying objects' and the task of an optimal solution for the problem to get them in close proximity... Obviously you don't receive a Lenin prize for pure mathematics.

The other part is content: Bellman dealt with the same problem. But Bellman equations are notoriously hardware-demanding. Pontryagin on the other hand gave necessary (and sufficient for some cases) conditions in a form much more accessible to pen and paper.