It's because if you say you take the bus it implies that you only need one and have no transfers. If somebody needs to go two cardinal directions to get to their destination they need two buses, ie they are lost to the American public transportation system and won't be seen until archeologists find their remains.

The hubris of those who wish to travel 7 kilometers or more using public transit in the States is punished. Those who wish to travel 5 miles swiftly learn that feat is only attainable in a a minimum of 4 hours or alternatively you can walk or bike and get run over at a crosswalk by a pickup with more blindspots than a Abrams tank.