This is why repeated attempts at reform legislation have failed in recent years, leaving the Postal Service unable to pay its bills except by deferring vital modernization.
(1) why引导一个表语从句，leaving......为一个v-ing短语做结果状语
(2) 本句译文：这就是为什么近年来在改革立法方面的各种努力都失败了，这也导致邮政服务不能偿还各种欠款，除了推迟至关重要的现代化。
