That's not really true lots of groups are generally insecure, they just show it in different ways and in different communities. This is an art/writing community so you're going to see art/writing insecurities. Go to a different community you'll see the insecurities for that thing.
But, as for why artists and writers seem particularly insecure: social media, the advent of the internet and general down turn from the days when artists were considered of high value trades. Artisty used to be considered a highly sought after career, and saying you wanted to be an artist would see you find a master artist, study under them and maybe even had a good shot at royal or religious patronage. These days saying you want to be an artist is considered something that will leave you forever poor unless you're one of the lucky ones so you're not going to find nearly as much support from friends and family. The same way saying you want to become an actor is often met with jokes about being a waitress or bartender. Add to that social media and how quick consuming art has become and the mentality that your numbers on social media are the be all and end all of your worth exasperating the insecurity when most of the time it's algorithm and luck. Think about how one book a year used to be considered a good turn over rate for an author, now we're expecting two or three unless you've already got a name and those books are a lot more transient than they used to. A lower bar for entry means that voices that never used to get in the door can be heard, but it also means the market is flooded, the consumer is overwhelmed with choice, no matter what your quality or skill it doesn't matter, it's all about luck in a sea of content, and you are replaceable within second unless you're an absolute giant with enough momentum behind you, which, chances are, you're not. Artist and writers are expendable, easily thrown aside and you have to be the absolute top to avoid that, and even then nothing is guaranteed. Not to mention art is often seen as a reflection of the artist and is often very personal, so judgement of that art becomes a judgement of you, whether from the consumer point of view, or your. So, what's there not to be insecure about?
