Wings have a very delicate engineering behind them. If the airflow over the wing is disturbed too much you can lose lift and stall the wing. Plus ice build up on engines and instruments could mean bad info to the pilots and not enough power to get out of it. This was a prop driven plane so those are airfoils too. Ice on a prop and you might have no thrust to keep going.
How would icing cause the plane to stall like that? Shifting the center of gravity towards the tail?
Wings have a very delicate engineering behind them. If the airflow over the wing is disturbed too much you can lose lift and stall the wing. Plus ice build up on engines and instruments could mean bad info to the pilots and not enough power to get out of it. This was a prop driven plane so those are airfoils too. Ice on a prop and you might have no thrust to keep going.
From a video about another incident with ATR 72: https://youtu.be/DOrK_5cZTlE?t=1692
This is probably not exactly what happened to this particular plane, but the section by this time code explores your question.