RE: Why are Germans so good at being nudists?
There are reasons for nudity and they differ from country to country. Definitely religion plays a role in some countries' lack of neutral/positive attitude towards social nudity, but for instance Croatia and Spain are fairly strongly catholic countries and German Catholic South is more religious that Protestant North, nevertheless Germany's most nude friendly city is capital of Catholic Bavaria, Munich.
In Germany's case I would think reasons lie beneath broad penetration of FKK-movement in the past decades and subsequent level of enlightenment in relation to nudity. Most secular countries in Europe being probably Czech Republic, Estonia and Latvia; none of them have any notable nude movements or general "clothing optional principle", even if in all of them nudity can be enjoyed in some spots.
Very hard to say what exactly lies beneath in natural attitude towards nudity in various countries. All in all, most of Europe is definitely open towards nudity in closer circles, like within family and so on. Many textiles may spent time nude at home, at cottage, in garden and of course where available, in sauna, when only family or other people one is very familiar with, around. In US among textiles there is much clearer prudish attitude towards nudity inside textile families and that definitely leads to broader gap between nudies and textile population. In most European countries many textiles can be nude with others if situation is suitable and not suspicious. In US or among Americans elsewhere I haven't noticed such readiness unless they have some prior nude experience or otherwise exceptionally open to new things.