Part of the reason they found little resistance is that Operation Dragoon happened two months after a successful landing in Northern France. You can imagine that most available mobile units which could be moved to deal with the Northern landings, which were a definite threat in existence at the time would have been moved there, as opposed to sitting around on the French Riviera twiddling their thumbs and getting a tan.

Now, imagine if Dragoon happened first. All those mobile German forces would, instead, be further South. Yes, the beaches would have been less fortified, and it would have been easier to get a toehold, but sustaining the beachhead thousands of miles from the major 'bases' of the US and UK against the German reaction would have been significantly more difficult. The Allies laid a 25-mile fuel line across the bottom of the English Channel to supply their forces, and still ran out. Can you imagine fighting off a number of angry Panzer divisions with just the fuel delivered by cargo netting?

The original intent was to split the difference, and do both landings at the same time, but there simply wasn't the transport capability to do it. And, I'd wager, air support was inadequate as well. As a result, Northern France was the 'less risky' option, where the Allies could bring all possible forces to bear, even if it was going to be the tougher fight.