Why are congressmen allowed to buy stock in companies they regulate?

This is not a conspiracy necessarily, but it makes my blood boil and it certainly looks like one. I was reading a Forbes article about the top 3 stocks being bought by senators in the last 3 months.<br><br>"They’re buying shares in companies positioned for a post-pandemic boom—and selling some Tesla."<br><br>How are they allowed to buy stocks in companies they regulate? I know it's technically legal because they disclose their trades, but it's insane that they aren't forced to put all of their money in indexes or something.