Why is it that people are so surprised that graphics design requires skill and knowledge*? Sure superficially there is nothing special in graphics design at first glance. Still, there is quite much to know to do a good job. This is the 21st century; everything has already been convoluted to the extreme.
Some of the tech you need to understand are actually very hard things. Let's take color management as an example. Color management is a complex problem, even in some cases a hard problem. The solutions that exist out there are only adequate, by no means perfect. In many ways the color management problem has many of the features of security, the weakest link in your color chain can screw everything up. To be able to manage all this one needs to know quite many things that are much more technical than most artists would like to be bothered with.
On top of the technical knowledge one also needs to understand basics of human psychology business and so on. But most complex of all a graphic designer is expected to have taste, something that most your clients lack. So why do I meet so many people who assume graphic design is easy?
PS: Answers from people with no experience in graphics design more than welcome.
* Such as how to divide a circle into 5 equal pieces. I didn't say everything is hard :)
I'm not a graphics designer, but I don't think the issue you're describing is in any way specific to graphics design. I think that if you look hard enough, you can find this is issue in any field -- I know I've seen it in software development, for example.
There's something in psychology called the Dunningâ€“Kruger effect, which I think is related. It is a cognitive bias that seems to apply to any activity, ranging from (e.g.) understanding a piece of text to being a doctor. The bias is that people who are unskilled at or inexperienced in any particular activity will overestimate their own skill level and underestimate others' skill level. In other words, being unskilled at or inexperienced in something not only prevents one from performing it, but it even prevents one from accurately evaluating anyone performing it.
Thus, if someone knows nothing or very little about graphics design, they are prone to underestimating its difficulty.
It's a simple answer really, low barrier to entry.
It's like the tagline from the game Othello, "A minute to learn a lifetime to master."
As a secondary but also important answer. Most people don't value or know good design. They think they do but they don't. They associate design with all sorts of other non-design related things.
To try and explain better I'll use an art piece I'm currently working on. I have a very clear vision of how I want it to look. I sketched it out, found the site to do the photo portion, got a model.
Talking to the model she wanted her hair down and curly. My vision calls for her in a one piece bathing suit with her hair up. Its a little flexible on the bathing suit, but the hair must be up.
She views it like a layperson --- "my hair looks good down and curly." I'm viewing it as a designer with a vision and countered her in a way that explains that --- "We need your hair up in a bun because we're going to be creating a lot of tension between you and the vase, as well as framing your face with your arms and weapon" to which she said, "Oh that makes sense."
My point is for 99% of the population, design is easy, because they don't know what design really is. They think if it looks good it is good whether it serves a point or not. They're perfectly happy with Comic Sans MS, a flyer from their Word Processor, and the most extensive photo editing being a filter in an App. And they think that's what design is. The attention to detail and thought process that actual designers do - the stuff that pushes boundaries and progresses society - is very rarely done and even less appreciated.