Speculating here:
According to McCombs website, the final deadline to apply for domestic applicants is April 1st (
https://mba.mccombs.utexas.edu/admissions/adm/)
Even if it's just a few people that waited until end of March to apply, the adcom still needs to review their applications and invite them to interview. I think that after they have the last crop of applicants in, they'll make the final evaluations and announce their decisions to all remaining applicants, including waitlist ones.
My
guess is that the cat will be out of the bag by the end of April. UT cannot be oblivious to the fact that other schools are finishing up announcing their decisions as well and their prospective candidates may be "stolen away."
My own timeline (international applicant, although residing in TX now): applied 1/15, interview invite 2/26, interview 3/9 - still waiting for an answer.
P.S. My UT interviewer told me that she initially did not plan to apply to McCombs and only did so in the very end of the process, after she was rejected by other top schools. Clearly, she was admitted.

There's still hope, people!
P.P.S. And then she said that two years at McCombs were the best time of her life and she's really glad she applied and went there.