HBV and HCV are pretty algorithmic, I agree, there are well delineated guidelines that most people follow (thanks to Anna Lok). For that reason, infectious disease is moving into the treatment arena. What's more difficult and cognitive is doing pre- and post- transplant care for chronic liver disease and acute liver failure. This area plus PBC/PSC/autoimmune have a lot of unanswered questions, but the solutions is usually non-procedural, provided the actual transplantation belongs to surgeons. Some are working on liver dialysis.
The rest of GI is also complex, but the solution is usually endoscopy. IBD is kind of an exception, being a translational hot topic and lots of medications based on immuno/microbio mechanisms. But the rest of GI (polyps/cancer screening, motility/IBS, GERD/esophageal, pancreas/biliary/advanced endoscopy) are much more clinical/less academic and involves lots of endoscopy. And no one wants to study IBS.
Hepatologists don't always perform endoscopy (defer to GI) or liver biopsy (defer to IR) on their patients, depending on how the hospital is run. Overall, hepatologists spend more time in the clinic than general gastro and less time in the endoscopy suite. So they get paid less than other GI sub-subspecialties usually. So maybe you can say hepatologists are a bit bitter and thus don't like to see candidates going into their field for the sake of going into the GI endoscopy suite.