why not AS number based prefixes aggregation

Hi, everyone: For routing scalability issues, I have a question: why not deploy AS number based routing scheme? BGP is path vector protocol and the shortest paths are calculated based on traversed AS numbers. The prefixes in the same AS almost have the same AS_PATH associated, and aggregating prefixes according to AS will shrink BGP routing table significantly. I don't know what comments the ISPs make on this kind of routing scheme. -yang