Because in Finland we have four official languages: Finnish, Swedish, Sami and Sign language. Swedish is used in all the road signs as well and all the Finns should be able to speak Swedish in some way because we learn it at school.
You will come across with this character in Finland. It's used for Swedish words and pronounced as normal O. Finnish words don't have å, we use always O, that's because Swedes pronounce O as U in many cases, so they need this extra letter...
Finnish Tarzan would yell :"OOOOOOLIOOLIOOOO",
Swedish Tarzan "ÅÅÅÅÅÅLIÅÅÅLIÅÅÅÅ".