Can I assume that 737s single engine taxi on the No 2 engine? If so, the force from that engine would push the left noeswheel against the base of its axle, which is apparently what caused the “abusive grinding” (great phrase!) of the axle and which led to its eventual failure.
That wheelie good picture shows the strength of the NLG, seriously impressive and reassuring
Well, yes and no - half of it broke, the other half took the load ! Unless the aircraft was at max take-off weight and max allowable forward CoG, the nose gear would not have been near its maximum or operating limit. I am sure the nose gear will have been designed to withstand the force from the remaining wheel if the other fails at max allowable weight, so it will be plenty strong enough.