There is no "must." The current system, although ridiculous, can always continue to operate.
The best system is 2 weeks of single game elimination at the better seed. Bids as now with AQ and AL. Field ranked 1-16 by PWR, no exceptions, no bullsh-t. If that matches up conference rivals, so be it. If Factory Derp University has to play at Tiny Liberal Arts College, tough sh-t. Play better next year.
8 1Rs; reseed; 4 QFs; reseed; F4.
Clean, simple, fair.