agree with both above replies.

By the time the parents in many cases get to the youngest one, they have changed a lot of their ways. sometimes trying not to make the same mistakes as mentioned, other times because they are worn out from parenting (for lack of a better way to put it) and have grown lax and a lot more easy going about the same issues that may have been different for the older child. Either way it sucks for you, I know...

I don't think you should see it as worthiness though, necessarily.