Because unless there is a physical barrier, you're already being recorded by people's smart phones, which are also HD camcorders and video phones.
If someone is using a smart phone or more traditional format camera to record me, it will be obviously pointed at me. I will approach them and we will have words. It would be a deliberate act and probably an obvious one.
If someone is covertly recording me, of course, I will not see it, but if such video is ever published, we will have words in court. And if they should fail to successfully hide their surveillance -- the camera falls out of their purse, whatever -- they run the risk of having both their property and their person damaged, a significant disincentive to engage in such recording.
However, if someone with a wearable camera has failed to have the common courtesy to remove it when entering an establishment, it is not obvious whether they are recording me, and they could be recording me without intent, merely because they (for some brain-damaged reason) record everything. It is a substantially different case, and apologies for rude use of wearables that are based on the ubiquity of camera-phones are not not valid.