Probably fitting board is one of the stuffs which you hardly see in Europe. May be there is no name for it.
What is the reason to go inside the restroom? Most people go there for urination or defecation. Or brush their teeth after a long flight. Anyway it is related to hygiene. Then, there is a person who wants to change there clothes.
However, unfortunately toilet's floor is not clear and may be no one wants to touch their feet even wearing socks. Especially European toilets are not clean as in Japan. Therefore fitting board is appreciated to persons who want to change their clothes inside the restroom.
However, these fitting boards are not equipped at every restrooms in Japan. Or equipped at designated cabin only.