TT, the SSPX changed because Menzingen changed direction, before any Resistance faithful left, and certainly not because they left. That is an historical fact.
What Menzingen and the SSPX always rejected - a purely practical agreement with modernist Rome-which they said would cause our death, would lead us to lose the Faith, would be ѕυιcιdє - this they now officially pursue, as is evidenced by the 2012 General Chapter resolutions and the subsequent rapprochement with the modernists eg the Huonder scandal.
Any change resulting from good Catholics leaving on account of the danger to the Faith is accidental.
As Archbishop Lefebvre said, it is the superiors that make the subjects and not the other way around. Any idea that good Catholics should stay in such a system as the Conciliar Church or the SSPX to make it more Catholic is a complete illusion. Stay in and speak out against the dangers to the Faith and see how long you last! Keep repeating the words formerly spoken by the SSPX bishops and superiors that a purely practical agreement with modernist Rome would be a disaster and would mean our death and see how welcome you are!!!