It's not really propaganda, it's a demographic shift of who uses the site and especially the major subs. Reddit always had a monoculture of sorts in the major subs, it's just new users who have a new monoculture have started using the site while those with the old attitudes (and who are frankly older) have moved to smaller subs or given up entirely.

Not a particularly surprising turn of events to be honest, nothing stays the same forever.