How come nobody survived Air Moorea 1121, yet other people have survived crashes from altitudes more than 90x higher?
I'm guessing you consider your examples to be crashes from "90x higher" because the initiating events happened at high altitude. This extra altitude was actually a good thing in these cases, because while the pilots lost most control of the aircraft, they were still left with partial control. The extra altitude gave them plenty of room to figure out what was wrong with the airplane and how to control it with what was still working. This allowed them to end up in more of a crash landing rather than just a crash. In airliners that really do crash from higher altitudes, there are no survivors.

United 232 was more of a crash landing. Although the hydraulic systems were lost, the plane was still trimmed for level flight and the pilots could use the remaining engines to control the plane. They had plenty of altitude and airspeed at the time of the engine failure to get the plane under control and figure this out. This resulted in the crash landing where about 2/3 of the people on board survived.

Japan Air 123 was similar in that the aircraft lost hydraulics but they also lost most of the vertical stabilizer. Again, this happened at a higher altitude which gave the pilots room to react to the issue. The pilots still managed to fly the plane for a while but ended up crashing into the mountains. The survival rate was less than 1% though this was partially due to delay in the rescue operation.

Air Moorea Flight 1121 lost its elevator control cable. While the pilot could have used trim to control the aircraft's pitch, the airplane initially entered a dive and 400 feet was much too low to recover from this. If the cable had broken at a much higher altitude it's possible the pilot could have regained control.

Another point to remember is that in a large airliner like the DC-10, the passengers have a lot around them to cushion the impact. In a small plane like the DHC-6 this isn't the case. A crash into the water also results in a much higher impact, and any survivors would have to be able to swim free to the surface.