I think it is due more to reflection than anything else. They see what they perceive as another cham and get territorial. Because of their size and humidity requirement they are best kept in glass. Also, can you imagine trying to feed them fruit flies and pinhead crix? You'd probably have more outside the cage than in! LOL!
:you see the reason i think glass is bad is that i have heard of chameleons that don't understand glass that they don't see it but they feel it they try to leave the cage over and over and push the glass with their face and can damage or deform their face over time. JK