I guess the SSPX haven't heard the adage about one rotten apple spoiling the entire bunch. They kept thinking that they could reach so many more souls by getting regularized, but with an influx of Novus Ordites who are contaminated with worldliness, they're just going to gradually contaminate the Traditional Catholics, especially the children. One of the hardest battles for a parent is to teach their daughters in particular to dress modestly, avoid modern worldly music, etc. ... but the battle is all but lost when these girls see other girls dressing immodestly and getting all the attention from the similarly-contaminated young men, while they are ignored or left in the corner by themselves due to (they think, and perhaps rightly) their modest dress. They then resent their parents for it, and the second they have a chance may rebel against Traditional Catholicism and perhaps the Catholic Church in general. They'll see that the priests permit this manner of dress, so why are my crazy parents more Trad than a Trad priest even?
Vatican II tried opening the windows to the world, and that was an unmitigated disaster, but I guess the SSPX have not learned ... unless this is all by design of the various infiltrators and destroyers.