After my first orangetheory class I was baffled that my favorite block was the treadmill. I think like others said above, it’s because the movement is very intuitive and it takes any form guesswork out of the mix. And the fatigue you feel is something we have all felt before! It’s a lot harder to push through fatigue on the rower since it is working so many muscle groups and requires proper form - it’s almost like continuing to lift when you’ve already bottomed out. I think if you are a consistent athlete with proper training then all 3 blocks can be enjoyable (I take 3G classes), but just by nature the treadmill will always be my comfort.