It is not true that the word bus originally refers to an elongated means of transport, but on the contrary.It is also not correct to think that a word has only one meaning.
Bus is even in itself a historical synonym for box.Dictionary of the Dutch language[1 says:
According to his distraction, bus is a term for box, and oldtime It is the name for all sorts of objects in which something is salvaged, including such which are now preferably rebued otherwise.
The Greek π ᬚ ξις became buxisin popular Latin, and that form was left in the old germ.In the Old High German BUHSA (in which the I of the second syllable is not visible); High.Bühse, nHD.Büchse; Mnl.Busse
The English word ‘ box ‘ has exactly the same origin.
That we speak of a letterbox is the reflection of the fact that this word is older than our habit to name things what can be called ‘ box ‘.
The earliest attesting of this word, we are already in 1850:
— The Gegotene iron letterboxes, with dancers cans of inbuses or drums, the introduction of which… In the main cities of the state… has become certain, Resol.V. 26 Oct. 1850 (e.g. Stbl. n °. 288).
The fact that a bus bears that name is also explained by the WNT to that effect: it has the characteristic typical of a coach:
At bus especially thought of an object that is more high than wide.
In very different applications.
Language is not logical, but historical and a consequence of coincidences that are generally dispersed by circumstances.A nice example is the word: orange. Every other language has the word for this fruit that appoints the color: orange, Aranja,…. Only Dutch has something weird: we call it China’s Apple.
This gives a wonderful historical insight into the reaction of the people when oranges started to appear here on the market.People thought it was something weird that they assumed it was supposed to come from a very distant country. In terms of distant countries, most people did not know many details, but they knew China. Or it may have arisen when a particular market Kramer wanted new fruits to occur more exotily than they actually were.
Hopefully this helps?
For the same reason that a shelter has no: no need.
In fact, it is often no more than a slit in the front door.
I also know that the furry thing is called a draught cat against the incoming cold on the other side of the door.
But that does not meows either.