Have these same breweries, that walked away from the CO Guild, stopped supporting the national Brewer's Association headquartered in Boulder, CO? ABInBev and MillerCoors are the largest supporters of this Association as well and the BA hides this fact.
The Brewer's Association, by law, is required to make their IRS filings public. Form 990 Schedule B lists the large contributors. The BA redacts this information (Schedule B) from public view. Form details https://www.irs.gov/pub/irs-pdf/f990ezb.pdf
The IRS instructions linked above note that making Schedule B public is generally not required. The spirit of this disclosure exclusion is intended to protect contributors to true charitable and religious tax exempts - not those that represent public foundations, political action groups, lobbying organizations or trade associations that organize beer festivals to generate profit.
Why would ABInBev or MillerCoors object to the public knowing what they contribute to the Brewer's Association?