At surgery, my BMI was 20, but my normal level is 20.5. You have to give yourself the best chance for long-term success with TDR, which is why heavier patients are typically not good candidates (in fact, I read that only 20% of low back pain patients are candidates for TDR for a variety of reasons). Your surgeon may not have wanted to operate based on excess tissue and blood loss, but you also have to think about the future stress on the new joint.
By the way, my weight at surgery was 140 at 6 feet tall. I am now back to my normal weight of 150.