1) You list data is crap (scraped/purchased/"borrowed").
2) Users most likely identified your emails as spam.
3) Your IP/domain has no reputation.
3) The Big Five email portals don't know you and/or correctly identified your emails are spam.
4) No engagement from your list.
5) No whitelisting/add to contact list instructions on opt-in to make sure your emails inbox.
The Big Five: