In the summer, the UV index is incredibly high in northern Europe, so actually you’re more likely to require sunblock in the summers especially.

In general, norther countries need more protection from the sun, not less. The rates of skin cancer go up significantly as you move north. My guess is partly cultural, but I don't know for sure the cause. When it is dark all winter, people want to spend as much time in the sun as they can during summer, perhaps. The fact that you also get more natural summer exposure due to longer days is probably part of it.