I don't understand why people are so obsessed with the 12% APR. If they had the money to run the most profitable signature campaign, leave $40k as collateral, charged absolutely zero for mixing, and carried a shitload amount of money to begin with as we saw, then it doesn't preclude the possibility that they wanted to attract users via APR.
They certainly attracted several people in forum to leave coins received from signature campaign so they could earn a bit more.
It was suspicious to me when they first released 12% APR and I wrote about that publicly, but this is not huge percentages like we saw in regular scams.
Let me enter Speculation Station now,
I don't want to vindicate whirlwind or to justify what happened with them, but I noticed several people mentioned about similarities with Tornado cash service, and we know that escrow funds was deposited in DAI tokens on ethereum blockchain.
Now I saw one interesting news posted few days ago about recently arrested Tornado Cash co-founder Roman Storm, while fellow co-founder Roman Semenov remains at large and he is added to the list of sanctioned individuals.
It's not impossible to think there was some connection with whirlwind, and this could be one of the reasons for their/his absence and for service not working anymore.
https://www.justice.gov/usao-sdny/pr/tornado-cash-founders-charged-money-laundering-and-sanctions-violations