Why does “fliegen” not always happen in the air?

Question

In German "fliegen" is quite often used in a context where it has nothing to do with flying like a bird or with a flight by an airplane.

Kevin ist von der Schule geflogen.
Morgen machen wir einen Ausflug.
Wir haben das bei einem fliegenden Händler gekauft.
Die Zeit verging wie im Flug.
Die Polizei kam flugs zur Hilfe.

Was there a change in the meaning of "fliegen" over time, or is this expression used merely figurative here?

Side note: there is a similarly different usage of to fly in English (e.g. "to do something on the fly", "to fly away from something")

Answer 1

You answered your own question. It can be used figuratively to describe a rapid movement (not necessarily airborne) or, more abstract, a rapid change of a situation. You already provided a nice, diverse list of examples covering possible uses.

Other than that, it still perfectly describes the motion of an object that moves through the air. The implication is always one of rapid movement though.