It's a general problem with modern printing, especially with thicker volumes. At one time everything was bound using traditional bookbinding techniques, with sections individually sewn into what were called 'signatures'. These fell open and stayed open without effort. It's for that reason that desks on grands in particular weren't usually fitted with 'bookholders' (the swivelling metal pegs) to hold scores open - they were unnecessary with proper bindings.
Today, with rare exceptions, scores are bound using the same industrial methods standard for all paperback books. They won't open flat, and sooner or later fall apart. The fix is to use bookholders, which are easily obtainable. If you don't fancy drilling into your beautifully veneered desk, it's very easy, using the most basic carpentry skills, to make a 'false desk' of felt-covered board with a 1" batten for a ledge at the bottom, into which you screw the bookholders. This simply sits on the piano desk.