> In cases where they don't receive it though, they're not paying into it either.
If the "it" you're referring to is social security, this is, to use your phrase from above, "patently untrue." It would be comforting if that were the case, but there are cases where a person who has paid into social security will not receive anything from it, and will not receive their spouse's Social Security survivor's benefits, under WEP and GPO rules. As I explained above, I know one of these people and help her manage her money.
To the original point in my grandparent post: just having to do the math on this stuff could be deterrent to someone trying to make a decision about whether teaching is a smart career move.
> Maybe the union membership by in large doesn't want to?
WEP and GPO are a matter of federal law, although "maybe the unions want this thing that is obviously hostile to their members" is certainly... a thought a person could have. As it happens the American Federation of Teachers is lobbying to eliminate WEP and GPO, and I assume there are other unions who are acting similarly:
https://www.aft.org/resolution/repeal-windfall-elimination-p...
https://sports.yahoo.com/congressional-bill-may-soon-end-194...
(some potential disinformation in the second link, but the point is, this is a pretty active debate)
edit: It occurs to me that maybe you meant "maybe they do not want to pay into Social Security," which is probably true. To keep this in perspective, these teacher pensions which were considered an alternative/supplement to Social Security are a lot older than the WEP and GPO, which came along to kick those with these pensions in the nuts in the late seventies and early eighties. The teachers and their unions were already committed to the path they were on when the federal government changed the rules on them.