I can tell you one reason for a portion of them on the lemmy.ca exclusive blocks, having been here just a handful of months prior to the Reddit-exodus of June 2023.
Since lemmy.ca is a few years older than sh.itjust.works, there are some servers that were blocked back then, for spammers or trolls that no longer existed by the time sh. first came online. One particularly infamous example from the early Lemmyverse is wolfballs.
Oh and the request/intent to join announcement seemed to indicate that while Fedecan would be an infrastructural and fiscal host for sh., it was agreed the operational management of their Lemmy server would be largely left to the existing people. I suppose no harm in reviewing the differences if there's time to spend, but just trying to provide whatever context I can to your analysis.
(Fixed link)