Because there wasn't a legal basis for it then. Now there is, and A&M agreed to that legal basis just like everybody else in the Big 12. A secondary reason: the Texas legislature was in session last year, and Baylor had the option of working the political angle, which worked (despite what A&M and Texas claimed). With the Texas legislature out of session, Baylor had no other recourse.
A few quick notes concerning Baylor, Texas A&M and the SEC at this lunch hour:
1. Chaos in college athletics is now here according to The Wall Street Journal.
2. Orangebloods.com says the SEC wants all remaining Big 12 schools to sign waivers stating that they will not sue… and that’s not going to happen.
3. Baylor’s poor attendance, poor record and poor facilities are forcing it to throw out legal threats.
4. This writer for the International Business Times can’t figure out why more Big 12 schools aren’t threatening to sue.
5. Mark Bradley of The AJC looks at who might be next on the SEC’s dance card.