>>722945527
Only one Weaver was imprisoned in The Slab, IIRC, and it was First Sinner. From what I can piece together, First Sinner started the Rebellion but failed and got locked up. The rest of the Weavers, went into hiding in the Weavenests and Mount Fay in order to continue the Rebellion. Then the snails and Bilewater rebels joined the fight and they managed to lock GMS up.

Either they didn't really care about Sinner being locked up or they didn't have time after the Rebellion had concluded and just ditched. From the lore hidden in the Weavenests, it sounds like they knew the binding wasn't going to last forever and they fled to other lands (which is how some ended up in Hallownest, for example). Then the Conductors took over and kept the Choir going to keep GMS enervated while the few loyal Weavers (perhaps just Widow) stayed behind to help bust Granny out of jail.