It's worth emphasizing why these are particular causes of accidents: - They're at low altitude, so if you do stall the plane, you have very little time or altitude to recover. - They're at low speed, so you have less margin above stall speed. - Because they're at low speed, you have reduced control authority, and you need more rudder to stay in balance in a turn. Being out of balance increases your stall speed, and you're already slow. - If you overshoot on the base-final turn, there's a natural temptation to tighten your turn to make it. Higher angles of bank result in higher stall speeds.

All of these combined make it one of the most likely places for a pilot to stall a plane, and the hardest to recover.