How interesting - I guess it depends where you look. I posted something similar to this a while back (but probably named the title inappropriately) as I was amazed at how much I have noticed it since I was diagnosed. I swear I have never noticed it before, but now whether to do with coincidence or whatever, I see it quite a lot. There have been a few incidences now in restaurants, where people have openly tested and injected in public places. I also spent a few days with someone who (albeit discretely, did test and inject at the table when eating. I see no reason why people should hide away in the loos for example. I have found this very reassuring as if I was ever using insulin again, I know I would feel nervous in public, but seeing these examples has really helped me feel no need to worry should that ever be the case.
Maybe you just need to look more carefully, but trust me, it does happen!