Quirk et al. explain that those are exceptions, and exceptions don't disprove the general rule.
"[N]ouns which are plural in postmodification," they write, "are singular (number-neutral) in premodification. . . . However, the plural attributive construction is on the increase, particularly in BrE where it is more common than in AmE . . . The choice of premodifying nouns in the plural rather than the singular may be attributed to a number of factors, but predominantly to the fact that an entity has been institutionalized in plural form" (pp. 1333-1334).
Here's a little story for you. I used to work for the California School Boards Association. In a meeting one time, the CFO mentioned that, historically, CSBA was known as the California School Board Association and then said, jokingly, that at that time there was only school board in California! Of course, there were plenty of school boards in California when CSBA was formed.
The fact that Board Association was changed to Boards Association in the name of the organization is a reflection, I think, of people's grammatical nervousness about keeping the singular when the reference is plural. Even if they know the rule about using the singular in attributive modification even when the reference is plural, they may worry that other people may suppose the referent to be singular.