LogFAQs > #986208834

The forced auction is meant to quicken the game and encourage people to spend their money, both to build monopolies and to try to prevent opponents from doing so. If no monopolies are ever built yet players are allowed to maintain their bankrolls, which is often what happens without an auction rule (because then monopolies will only get formed by sheer dice roll luck + properties not being very expensive to buy by default), this usually results in a "stalemated" game. I would say this is where the core of the gameplay even lies; you're basically stripping out the soul of the game by not doing the auctions.

I can only guess that some people decided the auction process was a bit too involved/intense for young children initially learning the game to grasp and decided to simply omit that part of the rules when introducing them to the game, and doing so became a standard. Ironically, this became a big part of the reason the game gained a reputation for being a long, boring slog. A lot of the other custom rules people use, such as the ubiquitous "Free Parking" rule, also help prevent money from going back to the bank, which ultimately makes the game way "easier" and contributes greatly to creating stalemates.

I feel like if you're going to play the game with custom rules, they pretty much have to be rules that make the economy "harder" in a sense. For instance, I tend to feel like passing Go awards too much money and I could see it being lowered; also default property prices are generally on the low side and could stand to be raised.