There's a perfectly rational reason for shaken (車検), though most HNers won't like it. It's designed to help a few parts of the auto industry value chain, from manufacturers (who get a domestic market which is, basically, forced into a 6-year upgrade cycle) to smaller-scale exporters (who get a constant stream of perfectly usable cars for essentially scrap value, then resell them to emerging markets for significant fractions of their off-the-lot value, because "everyone knows" that Japanese cars last forever).