Supposedly, Meta has the data to support the claim that you (and I) are the outliers here. Staging is confusing to users, especially new ones, which is why jujitsu explicitly doesn't have staging.
In discussions with people who made jj, it deliberately does not have Git’s staging area / index as a core concept because that was confusing for users.
Not solely because it’s confusing, but because it’s a more powerful and orthogonal design. The usability stuff matters too, but it’s not one or the other.