This distro would have been the default under WSL. Not Ubuntu. Not Debian. Etc.
Most people would not have cared which distro. They would simply used what was provided. However, this distro would come preinstalled with Powershell, Edge, to name a few. To further that it would make it easy to install additional Microsoft software like SQL Server, Management Studio, dotnet, etc.
Simply imagine the vast majority of Windows users who have never touched Linux trying WSL for the first time and getting accustomed using tools they already know on Windows. It's likely Microsoft or their distro would gain some popularity.
While this would be common with WSL - users could also download the distro for a full install. Use what they are already comfortable with. However, if they do decide to use a different distro, they would likely have enough confidence to know how install Microsoft software on it.
Again (and thankfully) a missed opportunity.
In all, why do I care about Edge or Powershell or other Windows-based software or tools on GNU/Linux?
If there is general interest in using Edge - I, too, would like to hear it.