Problem solving is a skill,
you learn more every day.
The bugs are in there somewhere.
They don't just go away.
Details
The more problems you solve the more you learn about them and how to analyse them. You need to do something to make a bug go away.
Some bugs do appear to go away on their own accord. This is because someone else has fixed the problem in their code.
There is a tendency in modern projects to let bugs go stale. This is very annoying. It doesn’t help anybody.