Why must writing be so hard?

This is my first blog in this series. I've been a professional writer for more than 25 years. Over the past several years I have been fairly successful writing weekly columns about cooking. I've won a few awards in the process, nothing earth-shaking, but it makes me feel good about myself. I'm working on a culinary book right now, as well as a novel with a culinary theme, and am promoting a play I have already finished, also about food (specifically, chocolate). I get plenty done and have good work habits. The only problem seems to be that I must work in small bits, running out of steam frequently. Two hours of writing is a good result for a day's work, but it takes me ten hours to get it all done. I know when I don't have the creative edge, so I have the discipline to make myself stop. I guess because I put so much of myself into it, I burn out and must regenerate frequently. There's a cost to all this, isn't there?