If anything, shouldn’t it be encouraged, and even automated? I’m including even the ‘old’ stuff from reddit here. Reddit shouldn’t be the absolute owner of the content submitted by users. When I migrated here, it wasn’t because of me being against reddit users, but being against reddit the company. Copying the content here actually hurts the company in sense that they don’t get to then gatekeep the crowdsourced content.
This is unfortunately part of migrating. Not all communities can just move over. Larger ones will develop and with that side communities will start with a large enough user base. Reposting in this case still doesn’t do anything other than give you the exact same content as Reddit just now it’s without an interactive user base.