As a former college fundraiser, I can promise you that the cash SMU needs to finance facility upgrades, NIL inducements, increased travel costs, etc, is way, WAY beyond $10 mil per year. That is barely a down payment.
All of the reconstruction and improvements TCU has made to Amon Carter Stadium and its supporting facilities (training, compliance, coaching offices, team meeting rooms, film viewing, sports medicine, etc.) from 2008-present total more than $312 million. That averages about $20.8 million per year. And that's just for football stadium and program facilities -- never mind expanded staff, increased payroll (to attract best candidates), upgraded promotional programs for ticket sales, etc. Not to mentioned increased spending for all of these same expenses in basketball and the non-revenue sports, plus NIL, travel costs, etc.
You really think SMU donors are going to quickly bridge this gap? "Quickly" because that's all the time they really have. TCU has a larger student enrollment (especially undergrads, which is where intercollegiate athletics lives), a much larger fan base of both alumni and external constituents, a significantly larger endowment, and a much more storied and prominent athletics reputation, both past and present.
TCU has built these advantages through strategic vision, bold spending, herculean effort, and earned rewards -- not by groveling and prostituting itself, like some schools we could mention.