I have 101 reputation, but I'm still getting the message
Thank you for your interest in this question. Because it has attracted low-quality answers, posting an answer now requires 10 reputation on this site.
which makes zero sense. Why is this?
Question get protected either automatically, or manually by a moderator if they have been attracting low-quality answers. In most cases these questions will have several deleted answers from people who have posted spam / brief opinion-based one-liners (such as 'I like X because it looks nicest.' which helps nobody) or they attract lots of duplicate posts from people who haven't read all the other answers.
Protecting the question stops brand new visitors from answering that post, and encourages them to participate elsewhere in the site first in order to gain an understanding of what sort of answer works best for the site.
It requires only 10 rep from this site. That means one upvoted answer to another question, or asking a question that receives 2 upvotes. That's not a lot of rep needed but does give people the opportunity to get an understanding of what this site is all about.