Because there are different types of yoga practices. Out of that, bhakti-yoga is the topmost. Because Kṛṣṇa says, bhaktyā mām abhijānāti yāvān yaś cāsmi tattvataḥ (BG 18.55). Without being in the bhakti-yoga, neither you can be happy, nor you can understand what is Kṛṣṇa and what is your relationship with Kṛṣṇa. Evaṁ prasanna-manaso bhagavad-bhakti-yogataḥ (SB 1.2.20). If you want to be happy, then bhagavad-bhakti-yogataḥ, it can be possible. Nityaṁ bhāgavata-sevayā. That is stated, naṣṭa-prāyeṣv abhadreṣu nityaṁ bhāgavata-sevayā (SB 1.2.18).
This class is held for the benefit of the human society. And this is the process of nityaṁ bhāgavata-sevayā. Śṛṇvatāṁ sva-kathāḥ kṛṣṇaḥ puṇya-śravaṇa-kīrtanaḥ (SB 1.2.17). If you regularly hear about Kṛṣṇa.... Why regularly? Constantly. If we practice in such a way that we shall hear about Kṛṣṇa, talk about Kṛṣṇa, chant about Kṛṣṇa, eat about Kṛṣṇa, work about Kṛṣṇa, sleep about Kṛṣṇa, walk about Kṛṣṇa, that is Kṛṣṇa consciousness movement.