On D-Day why didn't the US paratroopers clear the German coastal defenses before the Amphibious landing started?

they did, the paratroopers landed the night before the landings took place on June 6th 1944

Answer That wasn't their purpose nor was it something they really could have done. The airborn landings were made miles behind the beaches. Their purpose was to take and hold various strategic points inland of the beaches and prevent reinfrocements from reaching the beaches. Airborn troops were really too lightly armed to attack and destroy such heavily fortifcations as existed on the beaches. Also if you had tried to drop them right behind the beaches like that, half of them would have wound up in the sea. Really, the only way to take heavy fortifications like that is with an assault by well supported heavy infantry.Michael Montagne

AnswerThe allies did expect the naval artillery and air bombardment to destroy the fortifications and they were generally right. At Utah beach most of the few bunkers were knocked out, before the troops landed.

AnswerThe Paratroopers goal was to drop behind enemy lines take out chaotic reinforcement troops, clear the artillery fixed on the beaches, and take control of small towns in Normandy to make it harder for the Germans to counter attack.

Besides I say Rommel did his part in fortifying Normandy. The only reason why it was a success was because the Allies fed the Germans info saying that they were going to invade Belgium.

AnswerCertain coastal defenses were considered to be of such importance that they must be removed to protect the beach landings.One worthy of note was the battery at Merville.Lt.Col Otway was given this job with his 9th Batt.of the 6th Airborne Div.He had a model of the target built with all its approach roads etc and practiced the attack,this all took place in a 2 month period before D-Day.secrecy was paramount and a number of pretty girls were introduced to the area with orders to extract all the info. they could from the parachute troops.In this they failed utterly,tho' every officer and man knew the whole plan,but not the location or date.Due to being widely scattered,as were all the airborne that night, his batt. of 635 which was planned as necessary, was reduced to 150,no mine detectors, 6 medics,no Bangalore's no 6 pounder,no engineers,one machine gun,no jeeps or glider stores,no mortars some signals.The C.O decided to attack. After destroying the battery,he had 80 men on their feet,30 casualties,20 of them stretcher cases.this is typical of paratroop warfare on D-Day.