The deal breaker for me was the underlying XML or SQLite formats of GnuCash. These are not terribly amenable to scripting, either for ingesting raw data or reporting. Whereas this is basically the point of plain-text tools like Beancount or HLedger. GnuCash feels too much like a walled-garden compared to plain-text tools.
The plain-text format requires more work at first, but after you get the hang of it (and provided you have some background in scripting software) it is awesome.