Melodic Minor Descending

Can ANYONE tell me why the melodic minor runs one scale ascending but runs a natural minor scale descending.

On the way up, an Aeolian (natural) minor scale doesn't use the leading-tone (natural-7th degree) so it doesn't draw us to the root as strongly as it could. When we add the leading-tone we get a harmonic minor scale.

e.g. natural minor A B C D E F G A becomes harmonic minor A B C D E F G# A when the b7 is converted to the natural-7th.

Now some consider the step-and-a-half jump from the b6 to the 7 to sound ugly, so they also raise the b6 to a natural 6. That's ascending melodic minor.

e.g. harmonic minor A B C D E F G# becomes A B C D E F# G# A when the b6 is raised.

On the way back down, we don't use the "leading-tone" to lead towards the root - it's the second note on the way back down, starting us away from the root. So on the way down we revert to standard natural minor & call it the descending melodic minor.

Alright, thanks a lot!

i assumed it had to do with the V7 chord for a perfect cadence or something