Why did the FIA resume FP3 at Spa with three minutes on the clock?

The third and final free practice session at Spa-Francorchamps literally fell into the water. Due to the huge rain showers that fell in the Ardennes and Lance Stroll's crash, the red flag was waved for a long time. With only a few minutes on the clock, it was still decided to resume the session in consultation with the teams. Why did the FIA decide to resume final practice after all?