[johannes1234321]

Check you are using proper rules. There are many house rules prolonging the game (no auction, money collected on free parking, uneven house building, limiting numbers of houses in the game, ...)

After reading the rules you can use the time they save arguing rules and why some wants to use house rules ...

[jedberg]

The limited number of houses is part of the official rules and also a key strategy. If you get a few monopolies and build them all to four houses, you block everyone else from building houses.

[blendergeek]

Houses and hotels are limited by the official rules. There are 32 houses and 12 hotels.