These native platform APIs don’t use GPU much, or at all. That’s true even on Windows where GPU support is better than anywhere else. wxWidgets wraps Win32 stuff, it does not use WPF (backed by DirectX 9.0c) nor UWP (backed by Direct3D 11+, Direct2D, and DirectWrite).

Count of pixels in displays was improving way faster than RAM bandwidth or CPU performance. Currently, this does not matter much on desktops, matters somewhat on laptops, and critically important for many mobile and embedded platforms.

When you want to render anything at all at native display resolution and refresh rate, GPU stuff is the only option that works well enough.