IIUC, TIOBE measures amount of discussion rather than use, applications, or anything objectively useful. So, OK, I can agree that a lot of people are talking about .NET. I'm talking about it, and I have ZERO interest in using it until it's included in the Debian package repository (which will mean I'm willing to trust its license). OTOH, I actively develop in 3-4 languaes, not all of which are from the Debian repository, but all of which I have reasonable trust in. And I occasionally dip my fingers in 3-4 more languages, which means I am willing to install them. Because they have licenses that I have reason to trust. (I'm not saying a reasonable license is the only requirement, but it's one of the set of minimal features before I'll even look at it.)
FWIW, my top 3 languages are D, Python, and Java. Ruby is in 4th place. I also occasionally look at Fortran, Haxe, Eiffel, Racket Scheme, SBCL, Squeak, etc. So my not being willing to look at C# is a strong indictment of the license. This doesn't mean my assessment is correct, but if MS issues a license that has ANY uncertain questions about it, I won't trust the license. Twice bitten, thrice shy.