Because there is only a fixed amount of land a city can ever possibly sustain. Urban sprawl all you want, but eventually you run out of land to keep expanding into or the city goes broke because there aren't enough revenue generating properties in a given area to cover the cost of servicing those areas. At some point more has to turn into better and more efficient.
If you think the time spent traversing all that space is completely worthless. Otherwise it makes sense to make things dense so that people can mostly reach whatever things they want to reach by walking a short distance or taking a quick tram connection, etc.
Because there is only a fixed amount of land a city can ever possibly sustain. Urban sprawl all you want, but eventually you run out of land to keep expanding into or the city goes broke because there aren't enough revenue generating properties in a given area to cover the cost of servicing those areas. At some point more has to turn into better and more efficient.
If you think the time spent traversing all that space is completely worthless. Otherwise it makes sense to make things dense so that people can mostly reach whatever things they want to reach by walking a short distance or taking a quick tram connection, etc.