The "names" you mention are more slogans used during commercial campaigns or related to specific events, than real given names.
It's like the "No way BA
-AA" painted on some Virgin Atlantic planes to fight the proposed cross-atlantic venture intended by BAw, while the given name on the same ac (this case G-VBUS) would be "Lady in red".
Why are airliners given names? Most likely due to a tradition inherited from the shipping business. Every ship had and has a name. Remember that in the English language, a ship is a she, a lady, hence a ship must have a name.
Aircraft are not much different.
A name gives a personality passengers can relate to. I remember my flights o/b B707 from Air France, all named from famous French castles: "Château de Chambord", "Château de Fontainebleau",... It had quite a style, particularly when being presented the menu with the picture od the said castle. These are now hunted by collectors.
The given names may refer to just anything, capitals, towns, lakes, mountains, saints, celebrities, royalties, animals, spirit of..., clipper ..., customers, employees, the boss' wife, fairy tales,...just anything (that's the fun of it).
As you can see, I do not have a straight answer to your question. I actually doubt there is one.
This question was raised several times on A-net, but I have been able to trace only one past thread:
If you are flying one of these ac your name refers to, I bet it has a name!