So why does quote-tweet and other forms of quote-posting not point to the original post like reply does?

In email, todays clients usually implement reply by first copying and quoting the entire content of the to-be-relied email first. Why is this behavior different on social? Maybe the default is fine, as the context is much more easily findable in social, but isn’t quite-post just a form of reply with the flag but please treat this is as a primary post like a normal one?