The Mara is in the middle of a sunny dry season. This makes for remarkable early predator viewing but later on these felines become catatonic. The plains crave rain wanting to be wetter than a Russian mattress (allegedly).
Wildlife requires patience and cats are intrinsically lazy, sometimes appearing as bored as guests at an over-hyped Washington party, so be prepared for a bit of shut eye. Give them time and they may perform, impatience will just deepen their slumber.
Please be sure to wish them good a night as you leave or, as they say in Swahili ‘Lala salama’.