Because the FSSP is in the Camp of the Forerunner to the Antichrist.
“A forerunner of the Antichrist, with his troops gathered from several nations, will fight against the true Christ, the only Saviour of the world. He will shed much blood and will want to annihilate the worship of God to make himself be looked upon as a God. Our Lady of La Salette 19 Sept. 1846 (Published by Mélanie 1879)
And the Forerunner to the Antichrist attends Gun Infested FSSP Masses and his name is Baron Alexander von Tschugguel
Put that in your pipe and smoke it!