Another reason is that many people don't value art in of itself. For them, art is merely a means to an end. A tool that if functioning properly, should bend to the whims of whatever purpose it's being employed for.
Take film. When people who take cinema seriously - filmmakers, aficionados, academics, film students - discuss questions like greatness and legacy, the conversation essentially boils down to one question: to what extent does a given film utilize those elements of the medium that make it distinct from other artistic mediums? Or put simply, what movie ... is the best at being a movie?
Not what has the best story? Not what has the best characters. Not dialogue. Certainly not revenue.
Think about the cinematic canon and the sorts of things that come to mind when various titles are listed off. The common thread is that these movies are remembered not for the stories (or lack-there of) they tell or the characters it sketches, but for how they go about these things in the context of the medium.
Godfather: the baptism/hit scene. Montage
The Passion of Joan of Arc: The close-up
The Shining: Danny navigating the Overlook Hotel in his big-wheel (camera movement)
Star Wars: Luke longingly gazing out onto the three-moon horizon (framing and blocking)
Many Great movies lack any sense of story *or* character, yet are still recognized for its greatness due to the ingenuity with which it exploits those unique elements of film: l'Avventura (literally "The Adventure", an ironic nod to how barren the plot is, it being a movie about boredom and malaise) , PlayTime, long stretches of 2001: A Space Odyssey. People love these movies because they love film.
Today, many moviegoers depart from this state of mind. They go not to enjoy a story being told in a way only film can tell it. Rather movies are just carrying cases for fan service. Their job is to recreate the experience of reading the book or comic as faithfully as possible, even if that means the actual movie suffers or that acres of potential is left on the table. People want to see the hero in the same exact costume they remember from their childhood. They want them to sound the same, fight the same, and act the same. They want the warm feeling of recognizing their childhood on a slightly larger screen. This is how they judge a movie, by its fidelity to an arbitrary, cold list of details. They care nothing for the medium.
Same thing with tattoos. For the types of people who browse forums like this, the attraction of a tattoo *is* the fact that it's a tattoo. We're not concerned with any one image. Our interest is in style (traditional, Japanese), and the history and culture that stems from them. As well, individual artists within those styles count for a lot, even individual shops. The actual images are usually of little importance. An image may matter only so far as it boasts an historical and spiritual connection with a style: hence no one here believes you can ever have too many eagles or skulls. Tattoos are not a means to an end for us. They are the end. We get tattoos to feel closer to tattoos.
Most people are like the comic book movie fans, though. They see it as a vehicle for their purposes - purposes that exist outside tattooing. They want a Star Wars tattoo so they can communicate to the world that they love Star Wars. That's the end game. The quality is of little importance. Who cares who the artist is? What matters is that those around them recognize the picture on their skin as Star Wars. That the work is shoddy and longevity questionable is irrelevant. The goal for other people to go, "Hey. Star Wars!" You don't need to do any research, spend much money, or give really any damn about the art of tattooing to achieve those ends.
Or maybe it's a memorial tattoo. Sentimentality does not require artistic quality.
Or maybe that want to look tough. In our society, tribal tattoos are associated with masculinity and thick-necked gym rats. People get tribal assuming these associations will graft onto them. The quality is irrelevant. All that is required is that people *recognize* the tattoo as tribal.
It goes on and on.
It's a sad state of affairs, that art has been reduced to its capitalist utility, meaning its ability to allow for people to assert their identity and self worth to both themselves and those around them via association with consumer products, taste, and arbitrary distinctions like nationality. We're all walking advertisements for our own desperate grasp at individuality and humanity under a system that by design undermines both, and to this end tattoos are one genre of marketing.
Taking blood is exactly that: it's literally sucking the life force out of you. I can't look because the sight of my blood being siphoned into that beaker makes me noxious. No such issue watching a tattoo needle do its work.