Why C++ now? Still the fastest and tons of quants and highly skilled programmers know it. When you consider the correlation between C++ developers’ technical acumen and quantitative skills, coupled with the maturity and increasing convenience of the ecosystem, it makes sense.
Which is not different than being locked into e.g. JVM family, or even being locked into OCaml itself.
VCL is only available to corporate shops and those that aren't into FOSS religion.
MFC is in maintenance mode, and so far Windows developers are more keen moving into one of .NET UI stacks while keeping some C++ code as COM/DLLs or even C++/CLI, than jumping into UWP/WinUI. It remains to be seen if WinUI 3.0 will change the migration trend.
Then on mobile OSes, it isn't even an option, unless you want to write your own GUI from scracth using OpenGL/Metal/Vulkan.