Texas was never invited...Oklahoma wouldn't come without Oklahoma State...Virginia Tech wouldn't come without UVA. South Carolina was going to block any attempt to go after Clemson, Florida was going to block any attempt to go after Florida State and Kentucky was going to block any attempt to go after Louisville.
So, the SEC wanted Texas A&M, and had to take someone else to balance out the divisions. Missouri was so happy to go somewhere that they pretty much would step in line with whatever the conference asked them to do. They were on the outside, looking in, and their patience wound up paying off for them.