It will be interesting to find out if this was due to metal fatigue, stress, maintenance, etc.
There are so many old 737s flying around (some of them with me in them), so this could affect a lot of aircraft.
My educated guess: The landing gear wing spar could have had microscopic fractures due to a combination of heavy landings and metal fatigue and could have just given way as the plane was being loaded with fuel. Another possibility is that the landing gear trunnion bolt could have had microscopic fractures or improperly installed( least likely).
It would be crucial to know when the last landing gear installation was made, the last NDT inspection and if possible, the landing loads of at least 5 previous landings. Also need to ask the last few dep crews' whether they saw that particular landing gear oleo leaking during their WACs. ( Very common) If it was leaking, then the absorption force would have been greatly reduced making every normal landing a hard landing, thereby leading to the wing spar being damaged.
It's time MAS retired these 734s as they are beginning to show their age. Some have a knitwork of doubler patches on their fuselage.
Interesting username you have.
Do you fly one of them ?