Per the report
"Under the Policy, the “standard of proof required to find that a violation of the competitive rules has occurred” is a “Preponderance of the Evidence,” meaning that “as a whole, the fact sought to be proved is more probable than not.”
My guess is the term probable was used specifically because that's the language in the CBA (the Policy). They didn't want to go stronger because they aren't required too, and therefore less exposed for appeals.