I should have stated that this is my impression, but still the claim is not polemic at all. Microsoft dropped it and besides the popularity of CPython; IronPython and IronRuby did not find company-backed support. Instead, a small group of community developers worked on it further. Community work has often a bitter taste, because nobody is really responsible for fixing issues and finalizing a product. One of the largest concerns with Ironpython was the deprecated syntax. Finally, in 2021 the updated that, but in my opinion it’s too late. C# and Visual Studio has evolved so rapidly, that I would not miss developing .Net code with all the features you nowadays get from the combo.
Besides this, C# and CPython are basically my strongest languages, and I feel mixing both worlds is just not a good idea. Why do you need interfaces in Python for? That is a redundant language feature for a dynamic language with a different way of class inheritance. If I would only know IronPython, I really would struggle to understand the purpose many things. On top of this, you can not fully write .Net code with IronPython. There are simply language features which are not covered and which are extremely hard to come around. Maybe this has changed yet, but if I remember I had issues in declaring volatile fields, async-await syntax etc. Which is really a problem for parallel and concurrent programming…