matiasbalacco - yes, suction feed is only available from the wing tanks, so in the event of total electric failure, you will not have the wing tank fuel pumps running , ie fuel will only be suction fed from wing tanks. It makes no difference whether the fuel is coming from center tank or wing tank before it fails. So I don't think this is the reason.
Office Pest - It's not single source. The wing tank fuel pumps are running at the same time with the center tank fuel pumps, only at lower pressure. If center tank pumps fail, wing tank pumps automatically take over to supply fuel to the engines.
ASFKAP - Not sure about this. But it doesn't seems to be a valid reason.
FLX/MCT - Fuel recirculation for IDG cooling will be automatically stopped on take off and climb (FCOM1, 1.70.40, page 6 -CFM eng. only). So this is not the reason.
alwaysontime - Not true. Look at the reply to Office Pest.