Poop is also natural, but if everyone pooped along natural hiking trails, it would be a shit show. Established hiking trails tend to have many people walking on them each day, and disposing of waste along them - even organic waste - can have negative impacts on others experiences, as well as change local wildlife's foraging patterns. Just because it is organic matter doesnt mean it decomposes instantly - that apple core or orange peel could be there for weeks or months after you leave it.

Pack it in, pack it out.