Many 64-bit applications still use either a 32-bit installer or some 32-bit components. In comparison 64-bit Windows will support 32-bit (probably) forever.
Make that almost all applications. It's very unusual for a program to have a 64-bit installer, because it won't be able to control what happens when a user runs the installer on 32-bit Windows.
In practice, the only cases where 64-bit only wine will be useful are when 64-bit applications are packaged some other way (such as a .zip, Steam Play, or packaging specifically for Wine) or for running Wine builtins like msidb.