Feds indict John McAfee for cryptocurrency pump-and-dump fraud

Because he didn't intentionally deceive anyone as part of his "pump and dump". At least not in any manner where it can be proven that the deception was intentional.

In Musk's case, the "pump" was simply the very public announcement that he had made a large purchase --- which as far as we know was 100% accurate.

This is all it took for coinheads to start buying like crazy and "pump" the price. Whether Musk took advantage and made the "dump" is unknown.

Deception for personal gain is called "fraud" and is illegal. But there was no known fraud in what Musk said. Being truthful for personal gain is legal.