The percentages are not the most important. Concentrate on other things, but percentages are just for fun

So, the only contributor was Jiten Gore, who started the course out with a blank tree. Since the tree was blank, he had to start the course from scratch, and as you could imagine, that takes really long, especially with only one contributor. Unfortunately, he never contributed very often, he never added contributors to the team, and at one point, he went AWOL. Finally, Duolingo staff removed him and made KananG1 Moderator in Jiten Gore's place, and added new members to the team. And the new team saw the tree, and the tree was really bad and not either very helpful or informative. The new team had to start the course all over again. And they recently completely redid all the skills teaching the alphabet. But they're at least progressing.

Apparently there was one contributor named jitengore who wanted to do the course by themself so didn't let others contribute, but then jitengore neglected the course and they had to get new contributors.