But there's another barrier for arrest, you can't tell if it's recording (or if there's a light, people will hack it/cover it). If 8 people around have glass, it'd be fairly difficult to notice all of them, check for the recordings, and take them.

I know miniature cameras exist right now but since they only function as a camera, there's not too much utility to always having one around. Glass though has a camera but that's not it's main selling point.