Source : https://en.wikipedia.org/wiki/Monopoly_(game)#Early_history
As another comment posted, that is the point of the game. It doesn't always work out that way with house rules people use (knowingly or not).
No, not the other board game
And then play for hours towards your inevitable victory.
But since the rules of the game only allow you to build if you have a monopoly, when a JV is formed, all owners should nominate one person and transfer their properties (within that monopoly) to that person, who then becomes the owner of the monopoly and can do with it as he wishes.
This leads to a lot of fun situations when there is conflict between the JV parties about the usage, or if the owner requires money for financing something else, and decides to 'backstab' the JV partners. Keeps the game entertaining for hours!
I would usually forfeit and leave whenever I wasn't first, and generally speaking so did anyone else.