As this image demonstrates direct bookings adds more to the bottom line and is good for business. More subtle benefits of booking direct are not covered, but they are probable more important. Hotels are going to many lengths to create benefits for booking direct - and the reasons have more to do with brand integrity than rates.
Hotels loose control and are worried that OTAs tend to treat room like commodities, The OTAS build their own brand at the expense of hotels and they own the data, often not even sharing the guests email at times.
Its all about control and hotels are making moves to take back control; after all they are the suppliers!