Theo says it's because if they drop $platform, they'll lose the devs that like working on $platform who quite possibly work on @other_platforms as well.
Change is hard, but I think it's worth a shot. And you never know maybe spending more time focused on real needs will create a better product from all the extra attention given to things that are work worthy.
And, the OpenBSD development team has contributed a lot to the software community, so it's extra frustrating not to get enough support back.
I'd expect that at some point it just stops being a fight you want to keep fighting.