That's pretty easy, to give the blackmail credibility. I could post that I hacked someone's twitter account and got compromising information. It could even be true and I could post screen shots or the information. They could deny it, I could be faking the screenshots etc. There's no real way to legitimize the secret hacked data unless one of the parties were to corroborate the information.

This way it's is now internationally well known and big news that these accounts were hacked, and it wasn't just some goofy tweet that they could say was an accident or something like that, it's part of a big worldwide scam.

That being said I doubt people use twitter dms for anything illicit anyway and this is probably just some 14 year old Malaysian kid that got a twitter employee's credentials in a phishing scam and figured the best way to make money with it.

The stock market stuff could be more profitable but much more difficult to avoid a paper trail and the hackers probably don't have access to equity markets anyway.

Nearly 100% chance they will say the hack came out of Russia, because almost all hacks are proxied through Russia due to the fact that there are millions and millions of unsecured machines running out of date bootleg copies of Windows 7 or even XP.

90% of hacks are coming out of SE Asia, but 99% of them look like they are coming out of Russia.

They had the goods and wanted to flex their power. Also, they compromised / bribed an employee -- they were on borrowed time by the nature of the hack.