With US investors getting screwed by ActM and the SEC being there to protect US investors, why would the SEC not take action against Ken?
Because they don't prosecute legitimate businesses unless they have deliberately flaunted legislation to scam, defraud, or avoid taxes.
The SEC have already shown their colours here. They have troddon softly with cease and desist letters instead of Police raids or InterPol/extradition requests. The Bitcoin economy now has official sanction in the US, no legitimate BTC mining business will be closed down if they follow SEC guidance after direct contact. Ken appears to be doing that.