... but there's no denying that the whole tenor of BYU's chances (and, relatedly, Big12 expansion in general) shifted upon release of the LGBTQ Athlete Ally letter.

I'll admit that the ADs/Presidents may have "gotten past" that issue and had the votes to expand, but I think it gave ESPN "cover" to play hard ball negotiating and served to poison the well.

Major things to blame for the Big12 not expanding (in no specific order.):

1) LGBTQ letter (in addition to my comment above, this also served to make the national CFB and Big12 beat writers hesitant to write any more pro-BYU articles/comments.)
2) TV partners not facilitating the process (especially ESPN) due to a) a lack of a slam dunk #12 team with serious TV draw, & b) ESPN already getting BYU "on the cheap" due to our Indy contract with them and not wanting to pay more for the product if they could find a way not to.
3)Texas Politics

Minor factors:

1) So many new or interim presidents at Big12 schools.
2) BYU not making any serious national noise in FB since 2009 and BB since 2011.
3) Big12 student organizations speaking out against BYU's addition.