Both WikiCities and Wikia have "wiki" in the name and were original; they made it clear that the network was a wiki farm.
"FANDOM" doesn't come even close to implying the site is a wiki farm. You can very well argue that they're shifting away from that mindset, but as I've said numerous times, why drag the wikis down into this mess? It makes more sense to branch FANDOM off into its own separate thing rather than forcing all wikis to adopt the FANDOM label.
As such I disagree with your comment over how this is similar to the rebranding of WikiCities to Wikia. The WikiCities to Wikia change was done to avoid people confusing the site with a wiki about cities. Changing from Wikia to FANDOM will cause confusion as people think the site is a fandom hub rather than a wiki farm as many communities here still view the platform as.