我觉得你的问题是,把状语从句中“主从句主语一致省略”的原则与“分词做状语”的情况混淆了。这二者并不是等同的。一般情况下,分词做状语的形式都可以改写成状语从句的形式,但不是所有的状语从句在主语一致的时候就可以改成分词做状语的形式。举个例子来说:
since he was hardworking, he got a good grade.(since 引导原因状语从句)
可省略成:since (being)hardworking, he got a good grade.
可改写成:being hardworking, he got a good grade.(现在分词做状语)
though he was hardworking, he didn't get a good grade.(though 引导让步状语从句)
可省略成:though (being)hardworking, he got a good grade.
却不能改写成:being hardworking, he got a good grade.
你问的这句话道理是一样的。这样可以明白吗?
希望能帮到你。