After enjoying the vast heavenly abode, when the religious merit which took them there gets exhausted, they return to the fleeting human world. Thus, taking to the life envisaged in the three Vedas, those desirous of endless enjoyment, remain subjected to the cycle of life and death, going and coming.
Krishna showed the rewards for rituals, only to reveal how flimsy they are. The foolish and short-sighted alone will woo them. The rewards promised are all posthumous, about which none can be sure. This itself is sufficient to eschew them outright. Dwellers in the higher regions have to fall steeply. This is a cycle.
We are already here as part of this cyclic process. Of what greater use are rituals then – an echo of Mundakopanishad (1.2.7). It is like grinding the already ground! The discreet will never be deluded by it.