The issue at Omaha wasn't so much the defenses as it was the terrain. The beach itself is fairly small and is domainated by high bluffs. Defenses on these bluff dominated the beach and can deliver plunging fire onto assaulting troops. The only way off the beach and off the bluffs are various draws. These draws were mined, choked with barbed wire, and defended by pillboxes, trenches, and concrete "Tobruk" fighting positions.
As for why the Omaha was chosen - Allied planners didn't want to land there, precisely for the reason I outlined. However, they needed a fairly wide beachhead - about 50 miles wide.
A wider beachhead was needed to fix the six assault divisions being landed on D-Day. It also meant more follow-on troops could be landed after the intial landing to help shore up the beachhead for the inevitable German counterattacks. It alsogave the landing plan some redundancy in the event of the landings at one beach totally failed.
They needed to land troops far enough west to get a foothold in the Cotentin Peninsula for future operations to capture the port of Cherbourg. And they needed to be far enough east to secure the bridges near Ouistreham, so the beachead could be quickly extended east for operations around Caen.
So, the Sword-Juno-Gold beaches in the east needed to be connected with Utah in the west in order to create a contiguous beachead that couldn't be broken up and defeated in detail. That meant landing at Omaha.
Is it also true that the bombing raids prior to the landing that was meant to take out, or lessen, the German defenses at Omaha were unsuccessful and therefore the German defenses were much more intact than at the other beaches?
