Some are based in 1 location and have semi-regular tours often to the same places, staying anywhere from a day to a week.
Think the most common reason are the ones where its a second job and they don't want to work near where they live. Some like that only work 2 to 4 days a month. Easiest thing if you see a profile of someone you like the look of is to put them in your hotlist and see if they come back to your area; if its someone you really, really, really want to see send them a message and if you want a 2+ hour booking maybe they will arrange a return visit for that.