An application that is not running with raised privileges should does not have access to the Program Files and Program Files (x86) directories. This is good for safety, you know.
Next, once an application doesn’t install in Program Files or Program Files (x86) directory rather than installing into %APPDATA%, it will not face the situation that it needs to load a specific DLL file in a complex folder environment, %APPDATA% is very clear.
In general, the 32-bit version automatically installs to C:\Program Files (x86), and the 64-bit version automatically installs to the C:\Program Files, only few application will be installed in %APPDATA%, to my knowledge, only Chrome installs in %APPDATA%.
In brief, why there is not a AppData(x86) folder, because it is unnecessary.