Do people really voice search for things like that? Aside from drivers going hands-free, I have never seen a colleague or friend use voice commands where it wasn't just for the novelty.
IME, the first people in my friend group who started doing it were the ones who weren't insecure about looking "uncool" (so a combination of unapologetic techies and people without low self-esteem). Afaict, that's the main reason that people don't use a feature that would otherwise save tons of time.
I'm not afraid of being seen as an uncool geeky, but I would never use it as I don't like to broadcast what I am looking for to all my neighbors, even when I am alone I prefer silence, typing now requires basically the same amount of time.
I still won't use "OK Google", because it's the new Bluetooth headset, only douchebags use it in public. Come on Google, how much do you lose by allowing custom phrases?
More than one would be good, but it's probably hard to explain to layman how to choose a phrase for which they can create an accurate model that's so cheap it can run continuously.
Also consider that people are less likely to use voice search if they are around others. So that might explain why you haven't seen friends/colleagues do it.