In flat calm conditions there is a strong tendency to try to absorb the impact with just bent knees because rolling feels unnatural without extensive training
Jumping a round canopy any attempt to absorb the landing forces by bent knees will result in one outcome for a novice - broken leg/s, it took an experienced person to be able to do a "stand up" as they were called. Judging the time of impact with the ground rush was the issue. The landing roll that was taught was not unnatural and didn't take extensive training, being shown once and a couple of practices was generally sufficient, we did ours jumping off a brick BBQ.