"Enjoyable" is a more specific word than "good/bad". "Bad" can refer to any dimension (of any object, not just art). Therefore, in cases where no context is defined, its meaning is governed by usage. In the context of art and art criticism, usage of "good/bad" typically refers to technical qualities and subjective execution, e.g. composition, color theory, emotion, communication, etc. Something can fail much of that and still manage to be enjoyable to a significant portion of consumers, though theoretically there would be an inverse relationship at the highest level. But such a state doesn't invalidate those metrics nor does it invalidate the experience of those consumers. Both are useful and valid in separate ways.
Composition is all about how to achieve enjoyable drawing. If you are enjoying, if it is not bothering you, then the composition is good by definition.
Same with color theory, it is a theory that is supposed to help you to achieve pleasant drawing.
Since there is more than one method to make something enjoyable, then something being enjoyable does not necessitate that all those methods were individually well executed. In fact, since enjoyability is so subjective and abstract and individual to each person, all "understood" methods of making something enjoyable could have failed, and a bunch of people could still find it enjoyable, and vice versa.
Ultimately though this is tangential. All I'm saying is that, while your average person is of course going to use "good/bad" basically synonymously with "enjoyable/unenjoyable", a professional, in my experience, uses the words "good/bad" more frequently to refer to more well defined specifics, for a broad range of professions. I only meant to explain why this website might use the term "bad" even though an individual HN user might find a lot of the art "good", and that it doesn't necessarily come down only to differences in personal taste.
(Though who knows? Maybe the website's curator just immediately thinks "I like that" or "I don't like that", and he leaves it at that when deciding what's "bad"!)
I've enjoyed a lot of things that are bad (e.g. poorly constructed, or 'well' constructed but only in a way that traps one-dimensional aspects of human experience to the point of inducing addiction). Now I look upon such enjoyment with regret. Your point is relying on the messiness of the word definitions; what fun.
