Elon Musk wasn’t charged by the SEC for offering to buy back all Tesla shares at $420, which is what I’ve seen some people on here misunderstanding. He actually committed quite a serious financial crime.
Musk announced on Twitter that he had the money (from funders) to buy back all Tesla shares for $420 each. This meant that if you owned a share in Tesla, it would soon become worth $420. At the time he made that tweet, a share in Tesla cost $341.99. Therefore, because he made that tweet, people started buying shares at that price, in the belief that soon Musk would be buying all those shares back and they would make $78.01 for every share they bought.
This caused a spike in the price of shares in Tesla, as everybody competed to buy up as many as they could. This increased the value of Tesla as a company.
However, Musk actually did not have funders secured to carry out buyback of all Tesla shares. He knowingly misled the public about the plans of the company, and financially benefited from doing so. Fuck him.