I apologize for the delay in answering.
As you pointed out, we don't have the limit of the number of human team members in the 2019 rules. It is because the main purpose of the Performance should be showing the robotic performance. It means that the moves of human team members are not mainstream in judging. We thought that subtracting some points with not a mainstream reason should be removed.
Also, each team understood this rule in their own view and there was a little difference between each of them. Sometimes, it made a small confusion in judging. We needed to avoid that situation.
Judges hope to concentrate on watching robots' performances.