Either they don't want to get their hair wet or their hair slows them down and they want to swim faster. That's the same reason olympic swimmers shave their arms and legs.
People who want to keep the sun out of their eyes wear hats. People who want the keep their head warm wear hats. People who just want to look cool also wear hats.
They wear normal clothes but some people wear Santa hats Santa clothes or elf's hats
People,soldiers,workers,cowboy.etc wear hats.
They wear it
people are not allowed to wear hats inside the church
Some people
People
There are a great many Germans that wear hats. There is no exact percentage or number as people change their preferences.
People wear clothes, hats, and sunscreen to block the sun.
Snacks
Nothing really, except they can wear hats
People where hats anywhere and everywhere, whether they use them to block the sun from their eyes or just as a fashion accessory.