I certainly remember a time when there were more Trads and SSPXers than there are now, but their disappearance didn't happen all at once. Verdugo's recent banned makes for a good case study, though. Who wanted him forbidden from calling himself a Catholic? Who wanted him forbidden from posting in Catholic Caucus threads? Who hounded him on the threads? Who (snicker) accused Verdugo of being me posting via a sockpuppet account? Who had something to gain by his being gone? Hint: it wasn't the Protestants.
As I posted earlier, no one gets banned unless they violate the posting rules on FR, and Verdugo violated them (I forget the exact offense), as did every other banned Trad/SSPXer whose presense we're now missing. Abuse reports are empty threats unless real violations are connected to them. Had Verdugo kept his nose clean, he'd still be able to post.
I’m not so sure that the disappearance was all at once. You’ve been here much longer than me, but I can piece together some information from reading older threads and communicating with current freepers. From what I heard, one reason may be that a few Traditionalists “outed” a certain freeper who was pretending to be a Catholic deacon.
Now, Verdugo was a special case. He signed up relatively recently and after the “golden age” of Catholic-SSPX disputes. I believe he was zotted for posting a thread arguing that all unbaptized babies go to Hell. After the majority of Trad freepers were purged, it seems to me that Traditionalist ideas became too “extreme” for this site, and his zotting is just one example of that.
As for who presented the most resistance to Verdugo? It was the Catholics. For one thing, he claimed to be Catholic not Protestant, Orthodox, Jewish, or Hindu, so naturally Catholics had to be the most forceful in disagreement with him. Also, he tended to focus mainly on Catholic issues and debating other Catholics. It seems that most Traditionalists, including him, feel that Protestantism is ridiculous and not even worth their time.