This sounds like uncertainty avoidance. Normally that term is applied to social groups opposed to individuals, but I am going to use it here because it describes the psychology behind the kind of fear you speak to.

https://en.wikipedia.org/wiki/Uncertainty_avoidance

I suspect for some persons perfectionism is a problem, but the frequency with which mental laziness occurs and the rarity with which perfectionism occurs suggests there are different or multiple motivating factors. Perhaps a common answer is that many people are unknowingly willing to sacrifice flexibility and freedom for familiarity and predictability. This is even evidenced by how people write software.