Everyone, please remember to be civil in communication.
We actually did a whole big survey and discussion with the community regarding this, and the community decided that only if a build is greatly overperforming as the result of a bug should it be fixed (nerfed) mid-season. Mid-Cycle Balance Survey Recap
For mid-season patches in general, we can only efficiently release patches part way into a season. This is because our internal codebase changes so much, that any bugfixes would need to be done in duplicate. One for the old code, one for the new code. However the real factor here is that these need to go through QA, and QA takes a fair amount of time.
This means that the the further we get into a development cycle/season, the more the codebases diverge, the more and more time a bugfix would take. Increasing to the point that it starts to significantly impact work towards a new season. Though we are looking at ways we might be able to get around this, as we understand how important bug fixes are, and how big of a topic this is for us.