First, your writing is very solid! :)
Second, I've had SOME stories curated, and they haven't necessarily gone viral - more Medium reads? Sure. Virality? Not so much.
Third - seeing that a story gets curated feels GREAT - so, I get that.
Stories that are at least a 3 minute read have a better shot, it seems. For me, the stories that have been accepted into publications have been more likely to be curated.
Stories with strong external links also seem to be more likely to be curated.
Yes, it's a bit of a mystery, but there are certainly things you can do to improve your chances. Submit to a pub. Include several solid external links. Be sure the story length is at least a 3 minute read - these may help.