The bridge is used every day... just mostly it's by TMs unless busy.
IOA as is could not operate without the bridge due to Potter being in the middle of LC and JP. Due to how strict JK/WB are about Potter, unless you are in Potter wardrobe, you better not even think about stepping into Hogsmeade or there will be issues. The bridge was built for the purpose of allowing all non-Potter TMs to bypass the land. It just also happens to serve a dual purpose in busy seasons.