I find this absolutely shocking! I started hitting $100/month at around 350 followers; on an "off" month I might make only ~$60, but I have less than 1k and you have 13k, so that doesn't make any sense to me at all. They must not be seeing your stories--which isn't fair! Medium needs to get their algorithm in order and makes sure they're putting the stories of people you follow in front of you. Otherwise, why have a "follow" function at all?

I think the more meaningful "follow" metric right now, with the current algorithm, is the email subscribers list. Only about 5% of my followers are also email subscribers, but at least I know that many people are getting a notification of my article.

Otherwise, it seems to be all up to Medium's distribution and featuring methods. I had what I thought was an 'okay' article go semi-viral because it was "featured" by Medium (got 900+ views in two days, earned over $15 in that time) but I have ones I think are much better, that only get ~200 views in a month. Quality isn't always the metric for success. Nor, it seems, is follower count.