Maybe a part to hype the fight that's why Ruiz is joining the party.
Remember recently, when Canelo trash-talk and insult GGG in their press conference which the latter didn't respond. GGG was surprised by Canelo's action saying it was unusual of him and not really necessary to do so in front of the media.
I like the attitude of GGG there not reacting to Canelo's behavior. Maybe GGG thinks that Canelo is still under the effect of his bitter loss against Bivol and may be shy to face him as he won his recent match against Murata.