This is an absolutely tiny site.

Things that work for small sites fall apart once you get 10~100 million+ people.

Look, I help do the actual user moderation for a large (10m+) subreddit, and it is a god damn nightmare. Plus, on top of that, we have to do automated bot detection anyways, because otherwise it's just neverending bot spam.

I worked on a site with 200M active monthly users. No captchas. It’s totally doable.

Reddit is actually a good example of having millions of users with no captcha. They “fixed” their problem with user moderation.

You chose to become a moderator, so it must not be that much of a nightmare.

EDIT: Reddit does have a captcha now. My guess is it came along with the other users hostile changes in the new design.

Reddit does require a captcha and has for a long time.

edit: They have for at least the last 6 years based on online questions. Long before the new design.

I see you are correct. They did not used to though.