At least for https://www.fi/ the case is that someone registered "www" as the domain name in the early days.
ai. 209.59.119.34 cm. 195.24.205.60 dk. 193.163.102.58 gg. 87.117.196.80 je. 87.117.196.80 pn. 80.68.93.100 tk. 217.119.57.22 uz. 91.212.89.8 ws. 64.70.19.33
It really did make sense for such a tiny place.
At least for https://www.fi/ the case is that someone registered "www" as the domain name in the early days.