Well, again it's the amount of exposure to English, and the kind of exposure, which is the key to Dutch proficiency. English and US films, TV (the BBC is widely watched in Holland), music -- all the kinds of things that speak directly to kids and teenagers. It's a small language community as well -- not speaking English won't get you very far in employment, plus there's the historical role played by Amsterdam as an international city, plus the number of English speakers in the country, and so on.
It seems to me that the larger the language community, the less likely its young people are to learn other languages to a certain level of proficiency or in huge numbers. It's not a hard and fast rule (look at Germany), but Italians, Spanish and French kids don't come anywhere near the top of the league for language learning (although my experience is that it's improving). More competition from homegrown cultural products, less need to look to English to improve employment prospects.
If British kids were exposed to French or German culture (for example) at home to the same extent, this would help greatly. But that's not something that can be enforced, nor is it likely to happen with the stranglehold that English-speaking culture has over the rest of the world.