Why?

It's a little surprising because a lot of advocacy groups focus their resources on problems with a significantly disproportionate impact the people they represent, and it's not obvious at first glance why this issue would disproportionately impact retired people.

Coloured people and gun owners also print things out, but I don't see NAACP or NRA putting their names on this amicus brief :)

Still, when it comes to supporting common sense amicus briefs like this one I say the more the merrier! If NAACP and NRA want to sign the brief too, let them :)

Holy shit, did you just say "colored people" in 2017? That's not cool, anymore, dude

I suspect it was a deliberate usage based on the expansion of the NAACP acronym, rather than a term one would normally use. In _this_ case, that seems relatively harmless.

I've definitely seen the acronym POC - people of color - used by awareness advocates in a non derogatory way. I don't think GP's usage is terribly archaic.