All art is a form of progression from crude to elegant. In fact, you can even see that there are relational forms inside that specific tag that also appear in some other more "elegant" tags. For example:
The M in HEMP:

Other Ms in the image:

There is a pretty clear language of strokes and movements between these characters. Some of these are done in paint marker, others in spray paint. Learning how to control a spray can is an important skill to hone. Often these people lack the space to practice this, and even practicing it (if they are a youth) can be viewed negatively within their own home. These could be part of an initiation process as well. I really don't know. However, to say that this is not "reasonably" art is, I think, disingenuous because art is a process that you hone over time. I don't think people go out into the street and write HEMP on a dumpster for no reason. They do it because they are either A) being initiated into something or B) practicing. The reason you would be out in the field practicing is because the activity isn't just about producing the art; it's about producing the art without getting caught.