Most serious Objectivists that seem to guide their lives closely based upon Randian theory can accurately be called religious or cultist. Sad, but true. Their approach isn't fundamentally philosophical or rational, as is mine.
This seems to conflate motivation and other aspects of psychology with ideas. I'm the first person to point out the importance of psychology, but I think the reference to "Objectivist" should be about the content of the ideas, and not the psychological style with which the person holds those ideas.
Since "cultish" is clearly derogative I don't imagine anyone is going to participate in a conversation by saying, "Why, yes, I'm a cultish-Objectivist." Given that, I'm not sure that it has any benefit. To talk about people who hold a set of ideas in a cultish fashion can useful - like Eric Hoffer in "The True Believer". And to talk about ideas that might lend themselves to being held that way could be useful - in my book on Progressivism I mention that. And to talk about a particular person holding a particular idea as if they were a cult member might be useful - particularly to a therapist. But I don't see the value of puting this adjective into common use with Objectivism.
I'd also guess that "Most serious Objectivists that seem to guide their lives closely based upon Randian theory" is a set whose members are mostly not known. We only know those few we are acquainted with, those whose posts we read on forums like this, and those few who are public figures. I'm sure that I was somewhat "cultish" in my approach to Objectivism when I first discovered it... and for psychological reasons. But I was an angry, rebellious teen and that was half a century ago and my psychology changed. Others may have simply recognized the rationality of the ideas and accepted them over alternatives but not even put them in a place of immediacy in their life, just as there are many Christians who are Christians in name only - attending a church once or twice a year and for 99% of their life being more rational than not in every other area.
If someone made a crusade out differentiating their very proper, non-cultish approach to Objectivism from all other Objectivists couldn't that be seen as a cult-like activity? (Just teasing.... not accusing :-)