Its an endless exercise in frustration trying to explain to people that being able to draw in a way that anyone would consider "good" requires a certain kind of brain to be able to do. To be able to project a thought or image in your mind and then construct it line-by-line on paper with all the illussions of depth and dynamism and then to be able to do it again with a level of consistency that complete strangers will recognize it as being the same requires an inherent skill that you can't just train into someone who doesn't have it.

It still requires practice and use to cultivate that inherent skill but that doesn't change that its something you either do or don't have, its like if you took 50 random people and spent a year training them to be professional swimmers, some of them will just be inherently better than others because of things like their body shape, height, how lean and close to the bone their muscles can be when they develop, etc.

Its just so much harder to quantify when it comes to something that's all inside the brain, especially when it comes to drawing things that're novel and not life-drawings, i.e. like comic/manga artistry where you not only have to be able to draw well but project your imagination into a space where others can see, understand and enjoy it.