Unclear why. But it is not uncommon for Microsoft to leave 'holes' in their offering soo that the partner network can fill them. Over 90% of Microsoft's revenue is partner-delivered. This often sparks great innovation outside of Microsoft walls.

Uno Platform promotes the use of .NET, so is therefore a tech-partner to Microsoft.

And with Hot Design (https://platform.uno/hot-design/) Microsoft's .NET Ecosystem becomes richer for a tool that no other developer ecosystem has. It is A RUNTIME VISUAL DESIGNER for .NET Apps. It turns the App you are developing into a Visual Design surface you can drag-and-drop components on, data bind,etc.