Neither is probably the political correct answer but the truth is that these often happened and went unreported or uncovered. Practically most M&A fail while genuine, real successes are far and few in between, almost a lottery. Therefore, the best possible outcome to ensure there is no gross negative or outright failure!
The cultural ramifications alone from a failed integration are enough to cause chaos within an organization can cause a deal to no longer maintain the same value especially if it leads to high expertise turnover.