Please read the NTSB report and all its accompanying submissions. Once you have read everything you will have read my explanation for how and why the fuel tank exploded. You will also see a long list of recommendations and actions taken by the NTSB, the FAA and Boeing as a result of the investigation. It makes perfect sense to me and the engineers at Boeing. If you still can't understand it, I'm afraid you'll just have to take their word for it. LOL.
You've just admitted that you can't follow the supposed evidence. Even Boeing has stated that the investigation has found no explanation of how or why an internal spark would have ignited the fuel mixture.
And you just proved you haven't read the report. Keep reading.