Thanks!!
Again, to the subdominant key.
I think it’s easier to adapt a melody to the subdominant key rather than to the dominant key.
The D♭ major chord is ♭VII if interpreted in Cm key. ♭VII is a very common non-diatonic chord, and sometimes, even playing the note Ti over that chord is acceptable, unless emphasized too much. It could be why the melody fits to the subdominant key this much naturally.