Some of the clients I've dealt with in the past were quite resistant to sharing data with us even when they were using our software & had raised a support ticket requesting the sort of help that required access to it.
The idea that these same companies would be happy with a microphone switched on all the time listening to everything they're saying and potentially sharing it with Microsoft (which is presumably what any sort of real voice control & using Cortana would entail) seems unlikely in the extreme.