How the concept of computer change over time?
The Online Etymology Dictionary gives the first attested use of
  "computer" in the "1640s, [meaning] "one who calculates,"; this is an
  "... agent noun from compute (v.)". The Online Etymology Dictionary
  states that the use of the term to mean "calculating machine" (of any
  type) is from 1897." The Online Etymology Dictionary indicates that
  the "modern use" of the term, to mean "programmable digital electronic
  computer" dates from "... 1945 under this name; [in a] theoretical
  [sense] from 1937, as Turing machine".


It seems the word computer was given a new definition in 1945 to the more familiar programmable computer we think about today. Words change meanings all the time, it's the evolution of language and as machine computer became more popular than human computers the term computer changed as well. 

Technically anything which can simulate a turning machine can be considered a computer so humans naturally can also be considered computers, but that just seems more confusing than it is helpful.