Shrubs and trees close to houses (?)

[EightFingers]

Why do people plant shrubs and/or trees right up next to their house? I see this a lot and it got me to wondering. Seems like with all the humidity and rain, plants should be located far from the house to prevent mold and promote air circulation. Might also help keep coqui frogs and bugs away from the house as well.
So, why do people plant so close?