Why Is Amplifier Output Usually Taken from Collector Instead of Emitter in Transistor Circuits?

I was taught as current in a circuit design flows from left to right and top to
bottom, but output from an amplifier is tapped from collector of a transistor, why not
from the emitter?

May be it helps to re read the theories of transistors.
And a amplifier has transistors it is just based on the design.

You should have been taught - that is how you read schematics - top to bottom and left to right - had nothing to do with current flow.

As for the output from the emitter - there is - Look at any push-pull amplifier ( usually class "B")

Consider that you have a water pipe running which has an inlet (From where water enters) & an outlet (from where water leaves the other end). Now assume that the base of the transistor is the tap on the pipe which will either block the flow of water or it will allow the water to flow through it. using this analogy you can decode the working of transistor, Assume that collector is connected to +5v & Emitter is grounded, if Base voltage < threshold vtg then it will not allow the current to flow through the ground but in this case you will get a high output at the collector & if base vtg>threshold vtg then transistor will turn on & it will allow the current to flow to ground (output at collector = 0v). So that means it doesn't really matter from where you take the output until & unless you are using transistor as a switch but it does matter when you are using transistor for amplification.

current can "flow" in any direction. It all depends on the layout. _left to right_ and _top to bottom_ is merely a convention.

And, output from an amplifier (I'm assuming you mean "bi-polar transistor amplifier") depends on the configuration. There are three fundamental configurations:

* Common Emitter -- amplified signal on the Collector
* Common Collector (or Emitter Follower) -- amplified signal on the Emitter
* Common Base -- amplified signal also at the Collector