Stack Exchange should be more proactive when a user continuously downvotes another user.

Example: I saw on https://travel.stackexchange.com/users/1810?tab=reputation:

This was triggered by "Arthur's Pass" user leaving the website.

60 reps mean 30 downvotes on questions (this user mostly downvoted on questions). That represents ~10% of the questions posted by https://travel.stackexchange.com/users/1810. Furthermore "Arthur's Pass" user has only cast around 150 votes, which means that 20% of their downvotes were targetting https://travel.stackexchange.com/users/1810. It is ok to disagree but I believe there is a clear downvoting pattern here.

Why wasn't some serial downvote detection mechanism triggered?