Hi

Ever wondered why a steel beam is placed on the inner wall in a cavity wall ??

Welcome.

 

The outer skin of a cavity wall isn't usually structural, it's primarily there as a rain screen.  The inner leaf bears pretty much all the dead and live loads imposed by the structure, wind, snow loading etc.

 

Years ago it was common to not even bother to fit lintels over doors and windows set in the outer skin, as it's not normally structural, but to rely on the door/window frame itself to support the masonry above, something that's caught out a few of the cheaper after market uPVC window people, with an unreinforced uPVC frame, which then ends up bowing under the load of the masonry above.