Why this Krishna conciousness movement simply advocates worship of Krishna.

Sometimes people ask why this Krishna consciousness movement simply advocates the worship of Krishna to the exclusion of the demigods. The answer is given in this verse. The example of pouring water on the root of a tree is very appropriate. In Bhagavad-gita (15.1) it is said, urdhva-mulam adhah-sakham: this cosmic manifestation has expanded downward, and the root is the Supreme Personality of Godhead. As the Lord confirms in Bhagavad-gita (10.8), aham sarvasya prabhavah: “I am the source of all spiritual and material worlds.” Krishna is the root of everything; therefore rendering service to the Supreme Personality of Godhead, Krishna (Krishna-Seva), means automatically serving all the demigods. Sometimes it is argued that karma and jnana require a mixture of bhakti in order to be successfully executed, and sometimes it is argued that bhakti also requires karma and jnana for its successful termination. The fact is, however, that although karma and jnana cannot be successful without bhakti, bhakti does not require the help of karma and jnana. Actually, as described by Srila Rupa Gosvami, anyabhilasita-sunyam jnana-karmady-anavrtam: pure devotional service should not be contaminated by the touch of karma and jnana. Modern society is involved in various types of philanthropic works, humanitarian works and so on, but people do not know that these activities will never be successful unless Krishna, the Supreme Personality of Godhead, is brought into the center. One may ask what harm there is in worshiping Krishna and the different parts of His body, the demigods, and the answer is also given in this verse. The point is that by supplying food to the stomach, the indriyas, the senses, are automatically satisfied. If one tries to feed his eyes or ears independently, the result is only havoc. Simply by supplying food to the stomach, we satisfy all of the senses. It is neither necessary nor feasible to render separate service to the individual senses. The conclusion is that by serving Krishna (Krishna-Seva), everything is complete. As confirmed in Caitanyacaritamrta (Madhya 22.62), Krsna bhakti Kaile Sarva-karma krta haya: if one is engaged in the devotional service of the Lord, the Supreme Personality of Godhead, everything is automatically accomplished.

Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Fourth Canto, Chapter 31 – Text 14