You obviously haven't looked into the activities they undertake.
ANGA is a lobbyist organization, so is the IPAA. Any environmentalist worth a damn will tell you what terrible organizations they are, spending their money corrupting D.C. with their evil oil mongering ways. ANGA is America's Natural Gas Association, IPAA is the Independent Petroleum Association of America.
They're associations, just like the AMS or the GSA. They have a large contingent of lobbyists working out of an office in D.C. that do nothing but wheedle money out of congress. The AMS works from 1200 NY Ave NW, just a little off from Capitol Hill. There are dozens of lobbyist organizations working out of that building, much of your list is there. The Council of Non-Profits is headquartered in that building, so is the Center for Lobbying in the Public Interest.
They trade favors, illegally on occasion, in return for support for their organizations. They fund lobbying efforts from their membership dues, in order to increase membership or obtain other methods of income. Grants get them a nice dollar sign to send out with their yearly statements. Look at how much money congress gave you this year! What the grant is for is irrelevant, if the people in congress wanted to give the AMS grants to study MLP, they'd do what they needed to get them. Some poor bastard with no self respect would stop paying attention to the weather and start surveying brony's instead.
They are not altruistic, they may not even serve the interests of their members. The AMA barely pays lip service to theirs. They get their real power from being sole owners of the medical billing codes the entire country is required to pay them for. Doctors are fleeing medicine in droves, but they stand behind that disaster of a health care bill as if it were going to make them all rich.
You think of them as societies of scientists, but that's like saying the US congress actually represents the people. Most don't even vote, nearly half that voted did so for the other guy, and the ones that did vote for them probably would have preferred almost anyone else to the corrupt pieces of crap they had a choice in.