In general, the value of the average web comic is low, not because the quality is low, but because comics compete with other forms of digital entertainment - memes, cat videos, funny gifs, etc. As such, the would-be subscriber is hesitant spending $1-$5/month on one artist because they don't get a lot of value back in return. In my research, a majority of people who subscribe to these artists do so as a form of selfless support.