BGP (Border Gateway Protocol) is an inter-AS routing protocol since it contains the subnet reachability data from AS. There are many various reasons the BGP router always choose the loop-free route with shortest AS –path length. Among them include, the router may contain one path or more to catch any one prefix.
When this happens, BGP can apply some elimination rules to catch the one route. However, a longer loop-free path is sometimes likely preferred than shorter AS–path length due to economic-driven reasons.