I've gathered the impression that Roy Clarke would write whether or not there was a market for his work. In one of the books about LOTSW, his wife described a holiday, fairly early in their marriage, when she was determined that he was going to relax and have fun, so she forbade him to take any writing materials. Instead of relaxing, he was more like a fidgety lost soul. He finally gave up, when to the local store and bought paper and pencils, and started writing. It's almost as though his brain is continually seething with ideas and he can't settle until he offloads them in the form of a script.