Personally, I find "it was a prank" extremely easy to believe. It's the simplest answer to the question "Wait, if someone compromised Twitter so badly they could tweet anything from any account, why didn't they try to move the whole stock market or start World War III?"
"Because they're young punks and didn't think of that" is a reasonable answer.
Prank hacking would fit with the monetization when combined with statements of "who would be dumb enough" that underestimates stupidity like the whole charge your iPhone in the microwave or Soupy Sales' "send in all of the green paper in your parents wallets" not thinking people would actually do it. Plenty of precedent but easy to see why they would feel no responsibility for anyone mindbogglingly stupid enough to do so.
"Because they're young punks and didn't think of that" is a reasonable answer.