I think
@Feek, or another admin team has mentioned before that a significant number (paraphrasing here) of bad sales are from members who have not participated/contributed to the forum sufficiently.
Hence by automatically revoking their access, they hope to reduce the number of these users selling items.
Some, of course, will post more regularly, but this may also reduce the likelihood of them scamming/poor comms.
I am getting fed up with this entitlement and whingey attitude though (not aimed at you).
The mods are being pro active and trying something. If you don’t like it, tough.
It is literally 15 posts every 90 days for goodness sake.