I don't have a problem with map codes.
But I would rather want to use it within an app such as Google maps, than go to a website.
Google Plus Code is already similar, but Google doesn't work so great for unmapped or off road, like hiking in the Drakensberg, or visiting a ghost town, or visiting friends in the rural area.
But at the same time I don't feel like looking up the map codes and plotting it out etc. and then share it. I will first need to explain to them how it works as well.
I understand why OP created the website and reasoning behind it, I am just not sure if it is convenient enough for me to replace my instructions in explaining where something is, even though the theoretically it should make more sense, in practice it feels like too much effort.
So I don't think the problem is the system, but rather people slow to adapt to it, unless it is really a breakthrough experience.
The other problem is that in the areas I do not have good roads and or rural, there is no reception as well, in other words can't access the website. Google Maps offline maps is more helpful here, even though with its sometimes limited data.