Because we don't want people whose profession is maximally exploiting perverse incentive structures to flourish. A society that grants outsized rewards to bad faith citizens is bad for everyone. The more influence those cheaters have over the economy the worse off we all are.

You should not be able to get rich to the tune of a 600% daily return just because you're insider trading. That doesn't incentivize sharing your information with the market. On the contrary that incentivizes delaying communicating your secret information until the last second to maximize the return on your unexpected information.