While some actions (like a minor player doing thousands of dollars in insider trading) may be paint-by-numbers, my impression is that substantial resources go into the types of investigations that can lead to massive settlements.
Although, in a case like FTX, it’s hard to get blood from a stone.
I suspect something similar is going on with the quadriga bankruptcy in Canada. CRA (Canadian IRS) did an audit and shared its results with the creditors’ lawyers months ago but nobody has heard anything about it yet: they probably didn’t like the penalties they’re being asked to pay.
The SEC only has civil enforcement authority, ie lawsuits. Criminal complaints must be referred to DOJ. They also tend to be much less creative than Justice at finding jurisdiction over non-US entities.
The entire reason crypto companies incorporate outside the US is to avoid SEC jurisdiction. But crimes against US persons are crimes wherever the company is located.
Perhaps the DoJ has already starting formally looking at FTX, et al, on their own. OTOH, I actually had never heard of FTX or Bankman-Fried before recently, and honestly still don't get what the hubbub is about. I'm skeptical how impactful the collapse truly is, beyond the rarified world of crypto enthusiasts, wealthy tech investors, etc. And given that its overseas, I really wouldn't expect (either pragmatically or idealistically) the SEC or DoJ to rapidly shift significant resources and attention to FTX; certainly not on the order of days or weeks.
That said, the SEC, which AFAIU would normally take the lead, is poorly staffed. The SEC leans heavily on automation, intimidation, and rapid plea deals in order to avoid resource intensive investigations and prosecutions; much more so than run-of-the-mill criminal cases that more immediately can benefit from the huge staffs at the FBI, ATF, DoJ, etc. So when prosecution and a prerequisite comprehensive investigation is clearly warranted and necessary, there seems to be considerable inconsistency in process and outcome. And that's before accounting for the fact that financial crimes can be very difficult to prove at trial, both factually and legally--just ask Donald Trump or the Church of Scientology, white whales renowned for beating countless financial related prosecutions and civil suits.