Why cant a F6F-3 Hellcat reach mach-1 on a dive?

I need to find out why a F6F-3 Hellcat reach mach-1 on a dive from 20,000 and 30,000 ft. Given information is Zero-lift drag is .0211, Wing area 334 sq feet, weight 12,441 lb, 1500 hp engine, Zero-lift drag at mach-1 .211, and propeller efficiency is .3 at mach-1