The SEC is a civil agency. It can't arrest anybody.
He has even been served a subpoena by the SEC while in the US before. He was forced to sit down and respond to questions. He sued them about it because the SEC is supposedly not meant to serve you in public, but I suspect he was a pretty tricky guy to serve at all. Early enforcement would have been good, and it maybe would have required a bit of force given what we know about his flight risk.
https://news.bitcoin.com/sec-files-action-against-terraform-...
“Apply” as in win a trial. That’s not quick. And it requires a track record of Kwon flouting the agency.
Scams will always exist and scammers will always find new ways to scam people, no matter how many warnings there are. Advance fee scammers find are now doing crypto giveaways in which a victim sends 'x' crypto in the promise of '2x 'more. Crypto is the latest iteration of penny stock pump and dump scams.