ते तं भुक्त्वा स्वर्गलोकं विशालं क्षीणे पुण्ये मर्त्यलोकं विशन्ति। एव त्रयीधर्ममनुप्रपन्ना गतागतं कामकामा लभन्ते ॥

te taṁ bhuktvā swarga-lokaṁ viśhālaṁ kṣhīṇe puṇye martya-lokaṁ viśhanti evaṁ trayī-dharmam anuprapannā gatāgataṁ kāma-kāmā labhante

They, having enjoyed the spacious heaven-world, their holiness withered, come back to this world of death. Following the virtues enjoined by the three, desiring desires, they obtain the transitory.

In plain words: Krishna says that after these people enjoy heaven, their good merit runs out and they return to this world of death. Because they follow the rituals only to get what they want, they get only things that do not last.