According to the same link you shared, enough people own second homes that 61% of the population has access to a friend or relatives home. That feels pretty normalized (compared to here in the US, where I live in a high-income area and only know one person with a second home (and it's a permanent tent))

I think you’ll find quite a few people have access to vacation lodging, but they don’t talk about it for one reason or another.

By "normal" I mean that it's .. normal, not exceptional. Nobody will bat an eyelid if you tell about your summer cottage. It's not some rare privilege.

Many summer houses have shared ownership with a wider family. Say, your parents got one and now you own it with your siblings, each getting their own time there or agreeing when to visit together.

Even when you don't own one, you will very likely have participated in the summer house culture. It's very much part of the mainstream culture like sauna is. Maybe you visit your relatives' place, or you may opt to rent a place for a week.

Personally I feel renting is the best option as you can visit different places each year and avoid the maintenance burden -- and they obviously need active maintenance. But some do prefer a familiar place where they can spend all their holidays, and in some cases all weekends too on top.

I think the point is that it’s not just the wealthy households. Not everyone wants a cabin but most people can afford one.

Less then 1/5 is still super normal.