I think part of the problem is that not everyone knows what a mini is.
I just sold a Brett mini on ebay (had it listed here but no/low offers).
First sale got canceled. Guys says he didn't know he was bidding on a mini. I relisted, capitalized MINI in the title, it sold again, I messaged the new buyer letting him know he had offered on a MINI. He says, Oh, didn't realize that but I'll take it anyway.
Here's the listing. Point is not everyone knows about this set.
https://www.ebay.com/itm/1975-Topps-...MAAOSwnEJgCgmy