Morty and all the other Kuatos only say "Open your mind", they don't say other things, but give this phrase meaning psychically. The original Kuato in El vengador del futuro (1990) could speak perfectly fine, this signature phrase was just something he repeated as advice to Quaid. There doesn't seem to be any reason the Kuatos can't say other things. Artistic and comedic decisions like this are not goofs by the writers. Rick and Morty don't live in the Total Recall universe, they live in a universe where Total Recall is a movie and also where kuatos are real but behave differently.