I can comment on the rationale!
If you look at our guide and scroll down to the rotation analysis section, you will see that I specifically tested this.
From the guide:
Raging Blow does slightly more damage than Bloodthirst and generates slightly more rage. Bloodthirst has a chance to refresh Enrage and thus increase Enrage uptime. Bloodthirst also has a shorter cooldown, so keeping it off cooldown as much as possible will result in a couple less Whirlwind filler uses during a fight. When it comes down to it, you could go either way with this and be fine.
I chose to keep bloodthirst higher in priority because in most cases it slightly edges out prioritizing raging blow at 2 charges when bloodthirst is available.
We benefit from having an automated system to test rotation tweaks across thousands of setups with different talents, traits, stats, etc. and then pick the rotation that most often results in a DPS gain.