wrenchbender
Probably explanation is they had no Performance figures e.g. in the manual or whatever computer system they use for anything other than 1+F. Less likely explanation is that they did have the figures e.g. for F3, but this did not permit a takeoff at the required weight.
In short, the speeds, Flex and Flap are all related. You cannot pick and choose, or alter any one of these in isolation. A little common sense might apply with a light aircraft, long runway, cool / low altitude and no terrain - none of which apply to MEX!
NoD