A lot of the newer products are not required to be greasable due to the materials they use. Products like Teflon and better machining all contribute. According to one manufacturer this is their explanation.

Over 90% of the new products coming through are now fully encapsulated, packed with high quality French Molybdenum Disulphide Grease. Full encapsulation offers zero movement in the ball stud, unlike the older style metal to metal designs. The full encapsulation provides for a smoother and quieter operation, and subsequent increased longevity.
Full encapsulation also means that there is no need for grease nipples. Many alternative brands offer encapsulated product, but still offer the provision for greasing with a grease nipple, which is unnecessary. If actually greased in these circumstances, the grease has nowhere to go, and if pressure is continued, greasing can result in the dislocation of the base plate and subsequent failure of the joint