What do courses have against GolfNow bookings?

I always book my tee times through GolfNow mostly because of the convienance of looking at multiple courses in the area and availability on one site. Sometimes good deals can be had as well.

Some courses tho become noticibly disturbed when you're checking in and they realize you booked through them. Is there a reason for this? Courses don't have to market themselves on the site if they don't want to.