French pronounciation is pretty tricky, and French is a very standardized language. So most places you go to in France, at least of bigger cities, people speak French very similarly to in Paris. People are not used to hearing variations.

German is a germanic language of course, which is the same as English. So if you speak English you already know one language in the same language family, and your guess of pronouncing it will be better than when you attempt French coming from the same skill level. Germans are also used to amny strange dialects - while many struggle with the Swiss and certain Austrians, most have heard it enough to make it work. So that might help them.

That said, there's individual variation, and English speakers are unusually good at understanding variations of English as everybody hears all kinds of English all the time. Many europeans struggle a lot more to understand foreigners doing their best to pronounce their language—it's not just the French.

That's my theories on the matter, anyway!