Why Are Appeal Courts Normally Reluctant to Change Findings of Fact

Why are appeal courts normally reluctant to change findings of fact made by a trial judge or a jury?

A) because transcripts submitted are normally deficient.
B) because of the operation of the principle of stare decisis
C) because not having seen the witnesses they are not well placed to assess the credibility of the testimony given
D) because not having seen the witnesses they cannot apply the relevant law
E) because they are limited in their fact finding capabilities by the Constitution