At that time, The Nine split off for many of the same reasons that The Resistance object to the neo-SSPX orientation. Only difference is that it was a temporary shift in +Lefebvre's thinking, and by 1985, he was solidly against any such cooperation with Rome ... whereas the neo-SSPX direction seems pretty set and not liable to change course, not to mention that the neo-SSPX have had the benefit of many extra decades of hindsight. When Wojtyla arrived, +Lefebvre and others hoped that perhaps Montini was a one-off and that things would return to more normalcy under Wojtyla. They realized after a few years that this was a misplaced hope.
That's like saying there's a "small difference" between walking off with $1,000 of your own money, and $1,000 of a poor widow's money. Talk about an understatement!
That "little" issue about hindsight makes all the difference in the world. +Lefebvre wasn't a sedevacantist, and for good reason. There was no reason to "go there" at that time.
And to this day, 100% of sedes worldwide haven't achieved a DARN THING they couldn't have done as non-Sede Traditional Catholics. What has sedevacantism achieved in 5 decades? Nothing.Show me a good fruit of sedevacantism, and I'll show you a good fruit of the Traditional Movement.
Back to +Lefebvre --
So he was trying to hope, while also having incomplete information about the depth and FUTURE length of the Crisis. You can't judge him the same as Bishop Fellay. Archbishop Lefebvre was just hopeful and optimistic, that this Crisis could be turned around. +Fellay on the other hand was maliciously ignoring 40 years of a FIRMLY ESTABLISHED NEW RELIGION, a NEW PERMANENT DIRECTION for the Conciliar Church.
Neither was +Lefebvre puffed up, saying anything like "I will succeed in ending the Crisis, where X had failed." +Fellay DID say this. He literally said he would succeed where +Lefebvre had failed.
Many Traditional groups have been tricked, scammed, and double-crossed by Rome over the decades. But ALL OF THEM were after 1983. +Fellay had access to that history of Modern Rome's betrayals and evil schemes, while +Lefebvre did not.
But how many have thought about that? Has the average Trad stopped and thought:
in 1983 there was only 1 Vatican II Pope other than the recently elected Pope John Paul II? I won't count JP1 because his reign lasted mere days. You're right: Pope Paul VI could have been a one-off. And the Crisis was only 13 years old. Not even old enough to drive!
Today, the Crisis is old enough to join the AARP -- pretty soon it will be able to retire with full Social Security benefits.