> Why would I look at just their trading revenue?

Why should you? Suppose you did a bad. Let's it was a side hustle where you took refurbished ipads and resold them as brand-new ipads. Over the past year you made $2000 in profit from doing so. The cops caught you doing it and fined you $10k. That sounds like a pretty serious penalty. However, you're also a bay area software engineer making $400k total comp, so $10k is a drop in the bucket. Should they fine you $200k instead, just because you happen to be a software engineer?

Because if these are trading actions that lead to these fines then a rational actor might decide against taking then in the future lest trading become a net negative.