Y'see, I get so bored so easily. I like to start with a clean slate each time. Sure, I'll have characters drop in and out of books but the main cast of characters always changes. Maybe I'm wrong but I think if had the same joe detective guy or gal, I wouldn't write them as well; I wouldn't do as good a job.
The rose is a rose, And was always a rose. But the theory now goes That the apple's a rose, And the pear is, and so's The plum, I suppose. The dear only knows What will next prove a rose. You, of course, are a rose - But were always a rose.