Says who? What's the penalty? Some silly fine?
Elon loves to do exactly that, he does it now just to style on the SEC with how rich he is.
First, off, this conversation is about triggering the poison pill. So in this case, it would trigger.
That's what the conversation is about.
But since you want to focus on incentives:
That's an immediate dilution of his (and his compatriots) shares until their combined percentage was 15%. Additionally, they can be subject to a shareholder civil suit by anyone who sold the them shares for any increase in value between the time when they sold the shares and the information came to light. Additionally, they can be subject to a shareholder civil suit by any shareholders for any decrease in value of their shares after that information came to light until endtime fuzzy. Additionally, a civil injunction preventing them from taking the company private, preventing their scheme from allowing them to do so and rendering their actions pointless.
Those are just the people who stand to make billions from any of those actions. The SEC can also pursue it's own charges, but since they won't individually make billions, they are less likely to do so.
For that matter, if Elon promised Bezos, Gates and Brin they would make money on the deal (as opposed to doing it because it would be fun) it would also not be something they could do. Promise is doing a lot of work there.