Why not lease the building, too? In the case of McDonald's I can imagine it's because only McDonald's wants the specific building (which looks and serves a purpose specifically like a McDonald's), but if it's a generic office building, why wouldn't you prefer to lease both the building and the land it's on (assuming you prefer to lease at all)?
When it's a generic office building, businesses frequently do lease them, unless they have so much free capital (like Apple, Facebook, etc) that they can build a custom building for themselves as a long-term HQ. But you're right with McDonald's and many franchises they have to build with a specific architecture style that's custom to their brand.
