Because meshes are using UV’s which are created for a special size/mesh/shape. When you want to scale the texture, you will also have to modify the UV (in your 3d program or with the upper mentioned texture coordinate node). So either just create special material setups (like the on above) or use bsp brushes (there you can change such stuff with just some few clicks), but bsp brushes are not recommended, as they are not so good for the performance 