Someone should invent a game, that while playing demonstrates how much monopolies suck for everyone involved (except the monopolist)

Not really, many many more people are B12 insufficient than there are vegans/vegetarians. And much of what B12 you get is because supplements are given…to the animals. See e.g. https://baltimorepostexaminer.com/carnivores-need-vitamin-b12-supplements/2013/10/30

“Made unusable”: that’s not how it works. Even with occasional vandalism, there’s so much more people positively contributing, that overall the map just keeps on getting better and better.