Pure personal experience with zero scientific knowledge:
I think the carnivore diet has appealed to people with digestive issues over the last few years (seems to crop up a lot).
Depending on what I eat (still figuring that out) I can have a pretty awkward stomach. Back in Sept last year we visited the in laws and camped in their garden for 10 days, so cooked on a BBQ, I ate mostly meat - steaks, prawns, sausages etc, had rolls and wraps and a bit if salad and honestly it was strange how fine my stomach was...
Energy wise I felt great. I did always have a nagging feeling of "is this healthy" going off though. I was brought up to eat salad or veggies with my meals so it felt odd not to (for the most part).
Maybe something to do with the various amounts of chemicals that are used on our typical western food staples and how that then transfers into the gut lining.