It's a life insurance company, but yes, they are large. About $560 billion in assets under management in 2020. This is a state regulator though, and state regulator fines are rarely every eye popping amounts. Ultimately for the thing they were charged with (failure to adequately supervise employees), this seems like an adequate penalty.
Yes, in the securities industry employees are required to report ALL their securities transactions and outside business activities to their employers. It doesn't matter if you do it in your spare time or not, anything you do that is securities related needs to be tracked under rules established by the regulators to ensure there are no conflicts of interest and in the name of professional integrity. Keith Gill did not do this, and was actively hiding his activities, which is why it's a problem. Mass Mutual got hit because the regulator felt like didn't have adequate supervision since they weren't able to detect his activities, which he hid by posting under pseudonyms and not using his real name.
No, it has nothing to do with how much money you're making. It has to do with how many trades he made that Mass Mutual was required to know about and didn't. If it was one trade they didn't catch, that's not as much of a violation as a pattern of trading that all went undetected. For the purpose of ensuring employees aren't committing transactions to benefit themselves at the expense of the firm's clients, this is a very serious issue. The whole investment industry is predicated on being able to trust the people managing your money, so that's why there's so many rules about monitoring employees.
If the media fails to explain things in a way that satisfies people. They will inevitably reject the media explanation, to form their own theories and conclusions. Necessity being the mother of all invention.
There's nothing questionable about the explanation here. People invent conspiracy theories because they're too stupid to understand the real situation. That's not an indictment of the media, but the idiots.