The engineers "thank you" comes in many forms. The fulfillment of the job. The privilege to work on cutting edge tech. The satisfaction of their customers. Their salary and so on and so forth.
Irrelevant
> The privilege to work on cutting edge tech
Irrelevant
> The satisfaction of their customers
> Their salary and so on and so forth
Irrelevant, that is/was part of their contract regardless of outcome (otherwise R&D departments wouldn't exist, failure tolerances wouldn't exist, etc).
Musk merely gave directive, he didn't implement or do this R&D on his own. Calling this Musk's success is like saying Einstein design and built the atom bomb thus he is solely responsible for the death of many a Japanese. But society doesn't take that point of view, instead only that he contributed to it, not that he owned it through and through. A good leader leads their subordinates, but they are not the sole factor in their subordinates achieving success. If a leader does not recognize their subordinates, they will soon find they have no subordinates to lead.