Why does the "resistance" need a leader when so many resistors are still going to sspx chapels?
Because most have nowhere better to go, most likely. How many SSPX people live close enough to a resistance chapel to make it their regular church home? How many resistance chapels have mass and Sacraments regularly enough for the same purpose? If you have children, are they going to keep the Faith attending Mass a few times a year, or once a month, waiting sometimes years for Sacraments? As for the SSPX, I think a lot depends upon the priest and who attends. If the priest is one of the old guard, and/or the faithful (those with the $$$, especially), are from the older days, the new stuff isn’t likely to take hold as much or very quickly.
I think there are a fair number who go to SSPX chapels because the other choices are involuntary Home-Alone or the novus ordo.