I would think that the desire for a dedicated spectrum for wireless microphones comes from how interference affects their performance. A crude example might be

I would think that the desire for a dedicated spectrum for wireless microphones comes from how interference affects their performance. A crude example might be to compare a wireless microphone to a wireless computer network. Whereas a PC may need to re-broadcast a "message" several times in order for the receiving station to contain a complete copy, this happens at great speed and the repeated messages aren't terribly inconvenient for the user. Imagine if an individual experienced the same complications whilst speaking into a microphone, only to be garbled by interference and requiring re-broadcast. Now imagine the same effect during a concert, where your favorite guitarist's riffs are intermittently garbled into junk because the wireless signal from his guitar is competing for dominance in a crowded spectrum. Someone may come along and correct any or all of this thought, but my basic understanding of spectrum and interference leads me to believe that it's the consequences that are operative here, not mass adoption.