Magister is a grossly underpowered '50s design with outdated, unreliable engines. Based on a glider, and considered to have good handling and few vices, thus often used in the day by flight demo teams.
However, a it's marginal aircraft on one engine with a power to weight ratio that would be unacceptable for current certification. IMHO, the big cause was attempting to maintain level flight in a steep bank with only a slight turn if any. The wings are unloaded, essentially producing little lift. Only the fuselage is providing lift and marginal engine power is inadequate to offset gravity.
Was the pilot fixated on something on the ground? Did an engine lose power? Why the heck didn't he level wings to regain lift?
Sad.