Neat. Been here nearly a decade & didn't know that downvotes are capped to -4 for example.
Generally voting signal to noise ratio goes: upvote, no-vote, downvote — allowing more downvote would most like have more negative than positive impact on the community.
Back when comment scores were public via the API, I retrieved the lowest-rating comments for each month. which was always -4: https://docs.google.com/spreadsheets/d/1IfbSDYVBXiHZCuMdHXgp...
Bonus histogram of comment scores calculated in 2014: https://minimaxir.com/img/hn-comments/distribution_comment_p...
I think the limit probably discourages long winded "all these downvotes are a badge of honor" comments. People who crave downvotes only get four. People hurt by downvotes only get four, too.