Here's the thing: every major program does things that they don't want to get out. Some are worse than others, but there's an implicit agreement that "what happens in Vegas stays in Vegas." And most of the time, it does. But when one thing gets out, an investigation can uncover a lot more. Few hands are clean.
Firing for cause is difficult... and it can be risky. A school can find grounds and threaten, but coaches can threaten right back. When all parties retain counsel, it becomes a legal game of who blinks first and who has the most to lose. Whatever the outcome, it's generally a costly win.