Hi there - I believe the simple answer is that the manufacturer does not want one single source of fuel supplying the two engines at such a critical time of the flight (takeoff). Most manufacturers prefer a dedicated tank to engine arrangement.
OP
Don`t know the answer either, but makes sense...
CERTIFICATION
You can't get the aircraft type certified using the centertank fuel in that way, that's a generic regulatory NO NO.
I believe you mean, that for certification you can`t have an engine running on one pump only. That`s what happens on the A320 if using the center tank. But also don`t know if that`s the reason, because if center tank pump fails, the wing tanks would feed the engine, since the 2 wing pumps are always operating. And there would be no interruption to flow, beacause its a question of fuel flow pressure. When center tank pump flow pressure drops bellow the wing tank pressure, you`ll have wing tank jet flowing down the pipe.