Bummer. I bought resale last year and got the magnet from disney. Maybe try reaching out to member services and see if this is something they can sprinkle some of that pixie dust on and get one sent to you.
We purchased Old Key West resale 5 years ago, and received the same magnet from DVC (even though we did not purchase direct). Nothing further on our subsequent resale purchases though.
We got magnets on first resale purchase also, the oval ones back in 2016. Came with the ‘four (or five?) pillars‘ letter and an offer of a call to familiarise myself with DVC with a CM.
Got a Tote on one direct add on, but the rest of the resales never heard anything which I would not expect to.
The above magnet came in Disney Files a few issues back and all members got it then. Heck, they even managed to post it out to the UK.
Got our Welcome package on our direct buy today. We lucked out with 2 magnets inside the backpack! Now me and the wife don’t have to fight over who gets it