It did say that explicitly. The original version of the game was "The Landlord's Game"[1], and it came with two sets of rules: monopolist, as you know the game and anti-monopolist, with a land-value tax. You were meant to play the game with the former rules, and then again with the latter to see how much nicer it was. It turns out that being a monopolist is more fun, so, over time, the game was shortened to just that part and gained popularity through a bunch of rethemes. Parker Bros. bought one of those rethemes, though not from Elizabeth Magie, the creator, but from some other guy who claimed to have made it.
I'm not saying I'm a fan of the game. But, in its defense, I've never played the nice version. There are probably few living people who have. Perhaps it's even more boring?
[1]https://en.wikipedia.org/wiki/The_Landlord%27s_Game