What obligation does UW have to listen to him? Better to make a fuss on Twitter and let this get to donors who will have a thing or two to say to the department chair and head of school/deans/provost/president.

As a public institution, UW has an obligation to take seriously and investigate allegations of academic fraud. Besides that they also have a reputation to maintain.

The reputation to maintain is why they will protect the insider over the outsider. Unless it is really blatant or the insider is really junior or new, universities will do everything in their power to silence the allegations.