Just a gut feel on my part but I think the Big12 wants UConn as a hoops only member ASAP and I think their hoops brand would add to the conference total (as much as hoops program can at least) but UConn of course wants to use their hoops leverage to get the B12 to take them as a full member, as they should.
That hoops brand is as hot as it’s probably ever going to be right now so it makes sense for the Big12 to kind of wait them out but then if/when things start to change in the ACC with the GOR contract getting older then the ACC may go after them as well.