Because we are living entities, part and parcel of the supreme living entity, Param Brahman, Bhagavān Śrī Kṛṣṇa, so, as Śrī Kṛṣṇa is by nature joyful, ānandamayo 'bhyāsāt (Vedānta-sūtra 1.1.12), similarly, we are also joyful. We are also seeking after that joyful life. That joyful life is eternally possible when we dance with Kṛṣṇa, not dance alone or dance with anyone else. So unless we get that position, there is no actually happiness. Because variety is the mother of enjoyment. That is an English proverb.
Just like when we eat, we eat the same thing, grain and milk product, but when it is made in varieties, lucī, halavā and other things, the same milk preparation and grain, but it is made into varieties, it becomes enjoyable. Variety is the mother of enjoy . . . if I give you a lump of milk, or lump of grain, that is not enjoyable. When it is made into varieties, it is enjoyable. Similarly Brahman manifested in varieties, that is enjoyable. That you cannot have in the impersonal Brahman. When we approach the personal Brahman, Param Brahman, that variety is available, and there we can enjoy. From there we do not return. Yad gatvā na nivartante tad dhāma paramaṁ mama (BG 15.6).
So simply impersonal Brahman realization, that happiness is not perfect, neither this material varieties are perfect. So brahma satyaṁ jagan mithyā. When we are fed up with these material varieties, we try to enter in the impersonal Brahman. But even in the impersonal Brahman, when there is want of varieties, then again we come back to these material varieties. Therefore we see so many learned scholars, sannyāsīs, they give up these material varieties as mithyā and enter into the impersonal Brahman, but without variety there, they come again to the material variety for opening schools and hospitals. This is the fact.
So āruhya kṛcchrena paraṁ padaṁ tataḥ patanty adhaḥ (SB 10.2.32). Because they have no information of the spiritual varieties in the Vaikuṇṭha planet, in the Goloka Vṛndāvana planet, they come down, because there is no bhakti. In the Vaikuṇṭha planets or Goloka Vṛndāvana planet, nobody can enter unless he's a pure devotee.