In the consulting business "I rewrote X in Y" blog posts only happen when someone takes the time to budget the project, because there is someone doing the math of developer time x cost per hour.
Then .NET Framework has been Windows specific for 20 years, there are lots of .NET libraries that are thin wrappers over Windows APIs, or interact with COM/UWP.
Porting them to Core means just rewriting everything from scratch, and if they are to remain anyway Windows specific, there is no advantage other than stay on reboot treadmill that Microsoft has started with the UWP/.NET Core (now backing off with Reunion), so they just keep doing .NET Framework as usual.