The Allies considered 4 landing cites: Brittany, Pas de Calais, Normandy, and the Cotentin Peninsula.

Brittany and Cotentin are peninsulas and therefore could be more easily cut off by the German Wehrmacht. Pas de Calais was heavily defended because it was the closest part of continental Europe to England. Pas de Calais also has numerous rivers, canals, and other waterways which could've made it difficult for the Allies to break out. Normandy had disadvantages too. There were no major ports to supply the landing army (this would later be ameliorated by small and portable Mulberry harbors until they could take Cherbourg.

Normandy is also not that far away from Paris, and the coast is long enough that the Allies could land several divisions without many logistical problems (stretching out the German defenders).

Source: Ford, Ken & Zaloga, Steven J. (2009). Overlord: The D-Day Landings.

The Allies were guessing that Germans would place their invasion defenses up at Pas de Calais, the shortest point from Britain to France. They even had a deception plan called Operation Fortitude, where the Allies created radio signals, tank tracks, and dummy vehicles near the coast to give the appearance of troops there under the leadership of General Patton (who was actually there).

The Germans did move some of their troops up to Calais, but the biggest consequence was not committing all their troops immediately after the invasion, believing that a second attack was coming from Pas de Calais.

Source: D-Day:Battle for Normandy, by Beecher (2009)

Some of the biggest factors were:

1. The type of beach that you could successfully land an army (in large enough numbers) limited the Allies quite considerably. Sand compaction and things like what the tide was like strongly affected what could land and how much time they had to do it in.

Soft sand would have meant armour getting stuck or simply unable to drive ashore (in a similar way to how the Churchill tanks at Dieppe got stuck in the gravel and the failure that caused).

2. Allied fighter air cover could only operate within a fairly short distance on the British coastline. In order for it to be effective and available they needed to be fairly close to the UK.

The same sort of thing is why the Allies invaded Salerno in Italy and not somewhere else.

3. The pas de calais was the shortest possible crossing but was also the most obvious place to attack and thus the most heavily defended. This meant Normandy weighed up as a better option.

Sources:

https://www.worldcat.org/title/d-day-from-the-normandy-beaches-to-the-liberation-of-france/oclc/59924504&referer=brief_results

https://www.worldcat.org/title/oxford-companion-to-world-war-ii/oclc/32364507&referer=brief_results

The Normandy invasion beaches were a pretty good place to attack.

The casualties (circa 10,000 casualties, 2,500 of which were deaths, out of 156,000 Allied troops involved) on D-Day were most heavy among the airborne troops, rather than on the Beaches.

Among the Beaches, the heaviest casualties were on Omaha Beach where the 34,000 US troops took about 2,000 casualties.

Casualties on the other 4 invasion beaches were lower. There were only 197 casualties on D-Day out of the 21,000 US troops who assaulted Utah Beach. The 25,000 British troops who landed on Gold Beach had 1000 casualties on D-Day. The 29,000 British troops who attacked Sword Beach took about 1000 casualties. The 30,000 Canadians who landed on Juno Beach suffered about 950 casualties.

The 13,500 airborne troops from the USA and Britain had about 3,800 casualties, (a far higher percentage than any of the units which landed on the beaches).

http://www.ddaymuseum.co.uk/d-day/d-day-and-the-battle-of-normandy-your-questions-answered

I'm surprised nobody else has said it, but part of the reasoning of the Normandy beaches was Operation Bodyguard (part of Operation Fortitude, the overall deceptions of the Allied forces), a series of counterintelligence and deception operations to confuse the Axis as to where the invasion would take place.

Operation Quicksilver was run by US General Patton, who was removed from command after he slapped shell-shocked soldiers and create a large controversy. Part of Quicksilver was the creation of a fake American invasion force the "First United States Army Group" under one of the most well known and respected generals of the time, this fake army was intended to mislead the Germans that the largest invasion force was going to land at Pas-De-Calais. This forced the Germans to step up their defenses, and thereby weaken their defense at Normandy.

There was also Operation Ironside, a series of counterintelligence actions done by the allies to force the Germans to beef up their defenses of the Bordeaux region, there was no action on this other than double agents leaking "intel" to tie up one of the more significant tank divisions in a region that it could not provide support at Normandy.