Linked from
The 7 pages that link to Fixed cost, each with the reason it gives.
Economies of scaleRelated: Producing more units spreads these costs across a larger volume.
Sunk costRelated: Fixed costs may be recoverable or avoidable; they are not automatically sunk.
Variable costCompared with: Its total does not rise with each additional unit produced.
Cost curveRelated: It sets the cost incurred even when output is zero.