Kentucky joined the confederacy after Missouri & is the 13th star.
Repost, here's your history:
http://confederateflags.org/fotcfaq/fotcfaq4/
The Big12 was good for Mizzou for one practical reason. Kansas & Kansas St were within driving distance & could meet at Kansas City. Ames Iowa from CoMo is a 4 1/2 hour drive, roughly the same as to Fayetteville Arkansas.
Drive to Nashville is rough equivalent (Vanderbilt is shorter) to Stillwater & Norman.
So beyond Kansas, Kansas St, Iowa St and Arkansas we're really looking at airplane distance to get there anyhow.
Consider this:
If Mizzou been in the SEC for the last hundred years, could you even seriously consider Mizzou then moving to the Big12?