If subordinate clauses can be placed before or after the main clause as follows:
They hid because I came.
Because I came, they hid.
Why isn't the same true for relative clauses?
They are types of subordinate clauses.
One never hears *"That the song is upbeat I love" as an alternative to "I love that the song is upbeat." At least, I never have.
Was it used at one time? Is it used now, albeit rarely?
On a side note, do any other Indo-European languages have this limitation?