A lot of the colorizations seem really poor. They don't even look lifelike. What are the technical reasons why some of the 'old' b/w photos seems much more re

A lot of the colorizations seem really poor. They don't even look lifelike. What are the technical reasons why some of the 'old' b/w photos seems much more realistic than the others? Is it the type of film or processing that were used in creation of the originals?