Not sure so much on the cargo culting aspect, but in essence, I am convinced that this phenomenon is effectively true.
If corporations were run entirely by lawyers, the likelihood that any corporation would take risks that would lead to innovation would be approaching zero. Of course, corporations without laws would run amok, but that's beside the point. I've worked at companies that were absolutely afraid to do anything that the legal department found troublesome, holding them back from risks that might have been worthwhile and wouldn't have been apocalyptic had anything gone wrong. It's a shame to see that happen, and I suppose that's why the current paradigm needs to keep generating startups in order to drive innovation. Though we really haven't been seeing much innovation as of late.
There may be some cargo culting of noncompetes, but it seems more likely that noncompetes are inherently in the best interest of the business from the point of view of the lawyers, and businesses see noncompetes as a sort of moat against competition. Both are fairly reasonable perspectives, though neither is necessarily true in reality, which is why businesses don't necessarily have to listen to their legal team on every decision.