There are several factors:

Operation Overlord happened before Dragoon - the allied invasion of Europe had been planned for years, and when it finally happened in 1944, it was an incredibly important moment.

Operation overlord was a much bigger event - there were far more troops involved in operation overlord than in Dragoon.

The timing of Dragoon - the landings occurred on August 15th 1944. At the same time, the Falaise pocket was occurring. This was covered extensively at the time, detracting attention away from Dragons success.

(Personal speculation) The Lack of resistance during Dragoon. THe beginning of 19 of the world at war features a war correspondent talking about how when the allied soldiers landed in Dragoon, they were met by a Frenchman with champagne. Compared with the battle of Omaha beach, the struggle for Caen and the bocage, the weak resistance to Dragoon has meant the battle captured the public interest less than the Normandy battles.

Sources:

The Summer of 1944: A comparison of overlord and Anvil/Dragoon