不及物动词为什么没有被动语态?是什么词变成被动语态时要加to呢

使役动词 make let have help
eg: He made me laugh. I was made to laugh by him.
)不及物动词 本身意义完整后面不须跟宾语
eg: Birds fly.(不及物）
She has done（ her homewoke）. Her homewok has been done .