Your family probably DID play with house rules. The problem is most people think they know the rules of monopoly, but the rules most people play by are actually house rules. There are two major house rules that people think are official which cause the game to take a LOT longer than it should:
Not auctioning properties. When a player lands on a property that is not owned and decides not to buy it, the property goes up for public auction, where anyone can buy it. This leads to it only taking a small handful of turns for everything to be owned, and causing rent collections to start shifting a lot more money earlier on.
Granting money for landing on Free Parking. This is often $500, sometimes with the fines and fees paid for tax spaces and from Community Chest and Chance cards added. This injects a lot of money into the game when it happens and can completely turn around a losing player's game.
With the properties being sold earlier, and the lack of that money being put into the game, the rules of monopoly are designed to let one player get an early lead, the ones who get the early properties, start collecting rent from them, and use that rent to buy even more properties and collect even more rent, bankrupting everyone else. Not following the auction rule lets property sit with no owner as a "safe" space to land on. Free parking adding $500 into the game just adds at least one more, usually two or three more, turns to the game unless it's only the person who was going to win anyways. Both of these house rules do nothing but slow the eventual flow of money towards the eventual winner, usually the person with the early advantage, and is the entire reason monopoly takes as long as it does. Even a normal game could be finished in an hour and a half... if the rules as written are followed.
Monopoly was invented to show the unfairness of renting property, that the people who rent end up with nothing, and the people who own just keep buying more until they have all money and property.