My version of the story:

The ISO had a leadership clique that had been in charge for decades but they based branches on college campuses and prioritized recruiting students. Students come and go, some of them are initiated into the leadership clique, but the old guard on the steering committee stayed the same. During the first Trump term the organization saw rapid growth and everyone wanted new blood in the leadership. The 2019 convention saw the victory of the Renewal Slate which pushed out the old guard.

But then a letter was published about how one of the newly elected Steering Committee members, a Renewal guy, had committed SA and it was covered up by the old guard. Every other scandal, including the ones that had ended with the expulsion of the perpetrators, was relitigated. New accusations came to the forefront. People started having serious doubts about democratic centralism and Leninism's ability to handle these scandals effectively. 70% of the organization (or at least of the 400-something who voted, from a membership base of 1000 or so before everything came out) voted to dissolve the ISO.

Since then a bunch of people joined DSA, a bunch more people stopped organizing, and some folk reverted to reading groups. PSL might have some ISO veterans who can weigh in on the similarities and differences between these scandals but as bad as both of them are the similarities are really bizarre. Either the U.S. left has learned nothing from how to protect comrades from SA instead of protecting the abusers, or we've learned nothing about how to constructively respond to such a scandal in a way that doesn't involve giving up on years of organizational work and losing all momentum.