Why does the melodic minor scale differ when descending.?

I have a masters degree in music and have yet to get a satisfactory answer. It is the only scale that is different when it is descending. Jazz musicians have abandoned the descending all together. It is just a natural minor when descending. Why don't you call the natural minor scale the descending melodic minor, because that would be ridiculous. A scale is a scale is a scale, it is a collection of intervals, not a melodic line. I think the theory books should be changed. The only reason ive heard (that i don't agree with) is that it is like resolving a V7 to i chord in minor. That it is like your resolving to a minor. You do the same thing with a harmonic minor, why is it not different on the descending. Id rather trust the jazz greats that played it the same way descending then an antiquated theory system based on music from 300 years ago!! If you have anthing to add please do so.