A lot of times companies file trademarks that they know they won't get in order to get it declared a "generic term". Once it gets that designation the company can use it without worrying about a competitor coming in and trademarking the term later. You still can't defend it from competitive use like a trademark, but if you own the domain or have created other artificial barriers to its use, then it's really never a problem

The word glass is too generic; its meaning has been used many times to mean something other than an internet-connected device that you wear on your face.