The Jesuits in the USA (10 provinces) have been averaging 40-50 novices per year total, according to the Society of Jesus (USA) website. A far cry from the days when they had that, and more, in every province.
The FSSP averages about 10-15 new seminarians a year in Nebraska, while drawing from a significantly smaller pool. It turns men away for lack of space. No doubt, the SSPX does as well. The Jesuits have far more resources on their side and yet harvest far fewer vocations per capita.
Catholic orthodoxy and tradition sells, to juring and non-juring Catholic men, alike.
The SSPX is outside the Catholic Church. Filling seminaries with schismatics is good news only in the hope that one of them will bring the SSPX to its senses and lead it back to reunion with Rome.