As XNA has proven, it is possible for very popular libraries to disappear. Why did people think differently?
May be because some people really like this library and like the way the things were done: convenience, effectiveness and efficiency. I don't know, some people just stick with that.
So, perhaps use what ever library you want and just be sure to adapt, however be very afraid of proprietary languages such as LotusScript, UnityScript, C++/CLR, C++/RT, UnityScript because if those die, it is such a pain to recode your whole project.
OK, in this list you actually can put whatever language or script used nowadays. Recoding is always a painful procedure and everybody want to avoid it. But, for instance, you as language vendor, could announce developers officially that current technology will be killed of very soon. Microsoft just drop off XNA about 2 years ago and they said nothing. This is the only reason, why do people keep asking, what happened to XNA? Why doesn't XNA work with Win 8? etc. Moreover there should not have been any rumors around at all.