If you can't guarantee anything for all the nodes losing power at the same time, that's really bad.
If it's just the write buffer at risk, that's fine. But the chance of overlapping power loss across multiple sites isn't low enough to risk all the existing data.
I disagree that it's bad, it's a choice. You can't protect against everything. The team made calculations and decided that the cost to protect against this very low probability is not worth it. If all the nodes lose power you may have a bigger problem than that
Power outages across big areas are common enough.
It's downright stupid if you build a system that loses all existing data when all nodes go down uncleanly, not even simultaneously but just overlapping. What if you just happen to input a shutdown command the wrong way?
I really hope they meant to just say the write buffer gets lost.