"Why do you need so much flow?"

It's the volume of air you are concerned with not the flow. Blowing out irrigation systems with compressors which supply insufficient volume *can* result in the air overriding the water and leaving water in the line which then pools in the low sections and bursts the pipe/fittings when it freezes.

CFM (cubic ft per minute) is the flow rate, not volume.

Once the water pools, would the continued air blowing through not push at least some of the pooled water through the pipe, until it no longer pools to fill the hose?