Because talent brings about pressure, from others and yourself, and then in turns makes the thing you used to love doing feel like a chore.
Take art for instance. It was my passion since I was a kid, I would draw every day many times a day. I just enjoyed the feeling of pencil on paper, of trying to make a pretty face or a nice flower. It was pleasurable, care free and helped to ease stress.
Fast forward some time and I became quite good at it, simply because I drew a lot. So people started putting expectations on me. In art class I always had to be the best otherwise people would tell me I was getting behind. Then, as you become good at something, you start to realize how much more there is still to learn. How there are so many others far better than you and how, even though you can imagine something, you can't translate it from your imagination to paper as well as you wanted to.
Time passes and you do your hobby much less because it now brings you stress. You don't enjoy the process anymore, you get frustrated, you're afraid of disappointing others and yourself, you become highly critical of every tiny mistake because that's what art school does to you. And then suddenly you realise: reality killed your passion and you're left mending the corpse.
Then, as you become sad with life's struggles and with your craft, you start to make sad paintings that no one likes. You hear your own father say that what you create is horrible and no one wants to see it. This only exacerbates your sadness and anger so sadder your paintings become. You look at what you create and weep for yourself, the tortured soul that created that. You remember the days of drawn smilling faces, nature, animals whilst you're looking at a painting of yourself hanging, lifeless, with nothing else for the world to take.
Being talented is a double edged sword and even though I consider myself talented, I still feel purposeless. I don't see a reason to wake up the next day. Sure, I may be reasonably good at paiting, and...? No one likes what I create and I can barely create anymore. Years of my life, the word "artist" was a synonym to my identity but yet I'm an artist who rarely creates and struggles horribly to finish a painting. What good am I to the world? What value do I have, even for myself? Living surrounded by sad paintings, no friends, no mother, no sister, lonely every day.