Looks like it's money-related.
In letter to ESPN, obtained by @TheD1Docket, informing ESPN of intention to withdraw Western Michigan from Diamond Head Classic sites “the global pandemic that has forced a significant change to our university’s policies and financial resources”— The D1 Docket (@TheD1Docket) July 6, 2020
In letter to ESPN, obtained by @TheD1Docket, informing ESPN of intention to withdraw Western Michigan from Diamond Head Classic sites “the global pandemic that has forced a significant change to our university’s policies and financial resources”