Bureaucratic intransigence is a really upbeat way of putting it. How about corruption through regulatory capture? Big auto needs to sell their over-priced parts. Why let people buy a $150 after-market part, when you can just call up CARB and have them make people buy equivalent $1,100 factory or OEM parts?
Wow, judging by the down-votes, people don't seem to realize how expensive CARB deliberately makes it to own an older car, regardless of how clean its emissions are.
EDIT: To further demonstrate that it's all about money and not about smog, you can get a "Repair Cost Waiver"[1] if you've spent at least $650 (on CA-approved parts, of course), and they'll approve your polluting car, no problem. All they really want is that $650 in the pockets of their car industry buddies and $XYZ worth of repeated tests in the pockets of the test stations.
1: http://www.bar.ca.gov/Consumer/Referee/Referee_Centers.html