1. Ease. Can minor parts which break down due to environmental factors be easily swapped out (things which wear or suffer from breakdown over time)
2. The parts make sense to swap-out (sometimes new items are more efficient and are better than repairing an old inefficient item)
3. Cost. The repair may not be cost-effective.
4. Environmental impact.
(others)
Example, I've had a washing machine break down and all it was either a plastic bit that broke, another time it was one of the switches. Those two things have extended the life over 5 years. Online forums help a great deal in figuring out what might be the issue.