Most of us like to bash Monopoly, or pontificate on how to "fix" it.
But consider the genius of this:
A looming design challenge in every game is to keep players engaged. If, on another players turn, players don't have anything to do, they get bored and have a poor experience. Downtime, AP, the like, are all problems.
How did Monopoly solve this?
The best things that happen to a player happens on OTHER players' turns. Not just some things, mind you, but the BEST things, the game winning things, (collecting rent)
In fact, you win the game on OTHER players' turns.
And the longer the game goes on the more acute this is.
Players are constantly engaged, in increasing amounts, through the entirety of the game (minus the player elimination). It's not so surprising it's maintained it's popularity. What other games do you know that accomplish this?