Lots of good information on:
10 January 2018 - Aviation news release - Transportation Safety Board of Canada
Basically insufficient airspeed to counteract torque roll at 300' when powering back up.
Why he didn't ask for & take a procedure turn is a question he is not with us to answer.
Perhaps he was always vectored to an approach and had to deal with energy management and tailwind on his own arriving at a remote airport.
TSB does not detail his instrument experience; so we don't know.