The (((elites))). Because they can group jew-noticers and anti-vaxxers with the flat-earthers, lumping us all as "conspiracy theorists" to discredit us via guilt by association.
Discussion
I strongly suspect that Flat Earth and related lunacies (secret hidden planets, directed energy weapons burning Jewish directors' homes in LA, chemtrails, reptilians, creationism, the list is nearly endless) are seeded into anti-Establishment groups by intelligence agencies and Jewish groups, with the obvious motives of making our side appear insane and therefore repellent to the intelligent and competent people we must recruit if we are to win.