Have you tried getting in contact with Medium? Try sending an email to firstname.lastname@example.org, with a link to some of your work and requesting some feedback as to why you haven’t yet made the cut.
Personally, I think the quality of your work is MORE than sufficient to warrant curation. Speaking as someone who has been blessed by the Curation Gods more often than not, I can’t fathom why you haven’t been.
I hope you’re curated soon, you deserve it! Keep up the great work.