"When helping our friends at a fintech startup, we saw that while they had spent weeks building an admin panel from scratch, their accountants seldom used it."
It sounds like your friends didn't talk to the accountants to ask them what they wanted.
It's more that requirements change faster than the engineers can respond. These internal tools often aren't prioritized, and the role of any ops team (e.g. accountants) is very dynamic.
At that particular company, the accountants would often come across new tax form data they'd need to track. Waiting on eng to migrate the DB was too slow.
So the solution that your friends came up with didn't meet the needs of the accountants, which is that the accountants have data which is very dynamic and your friends built a very static system. Again, not listening.
It sounds like your friends didn't talk to the accountants to ask them what they wanted.