The scale that is two scales
Melodic minor is not a scale: it is two scales. Think of it as a scale with an identity crisis.
For reasons I’ve never been able to figure out, theorists joined simple minor, only ascending, with natural minor or Aeolian, descending, then named the mixture “melodic minor”. The result is incredibly confusing, because this thing called melodic minor is not one scale but two different minor scales, and then the assumption is that we only use simple minor ascending, always use natural minor or Aeolian descending.
This has never been true, as this example below from CPE Bach clearly proves. And, by the way, CPE used the same rules as his father, JS Bach. In today’s music we generally come down using harmonic minor, true not only by the time of Mozart and Haydn but also clearly seen much earlier in the music of Scarlatti, a contemporary of JS Bach.