Because...TRADITION!!!
A blessing and a curse for college football. It's what makes college football the best sport in the country. Also, what holds it to an
insanely archaic mode of picking a champion. For years, the whole BCS concept was essentially held hostage by a parade involving floats made out of flowers. Which suited the "power conference" that LOVED to brag about how well it did everything EXCEPT football just fine. For some reason, big-time football couldn't use the same playoff-type system that literally every other sport used to crown a champion (basketball, baseball, hockey, soccer, lacrosse, etc. etc.). They couldn't even use the same system that every other level of THE SAME SPORT (I-AA, D-II, D-III) used because of the tradition of being rewarded for a great-to-good season by going to a good-to-acceptable location for a football game at which their biggest fans would gladly scoop up end-zone seats while local big-wigs would get the prime spots for their loyalty to the local chamber of commerce dog-and-pony show that the bowl system had become.
I also say "good riddance" but am eagerly awaiting the howls of protestation from the first team left out of the playoff system next year.