This little sidetrack woke up my curiosity so I found this: https://www.agicorailfasteners.com/news/what-wood-are-railway-sleepers-made-of.html saying
Common track section and turnout track section: Elm, birch, oak, jarrah, karri, sal, mora, maple, azobé, poplar, larch, pine, Yunnan pine (a kind of Chinese pine), spruce, fir, hemlock and other broad-leaved tree species (poplar isn’t used as turnout sleeper).
Bridge track section: Huashan pine (a kind of Chinese pine), larch, Yunnan pine (a kind of Chinese pine), spruce, fir, hemlock, koraiensis, etc.
The common nominator seems to be availability, using a local wood that matches the criteria for strength and durability. That's most likely why we have used creosote treated pine here in Finland. Pine grows naturally almost all over the country so there's little transportation costs. Birch is almost as common but it tends to rot so the choice is clear.