Although Lord Brahmā had prayed to take birth as a blade of grass in Vṛndāvana or even in the area surrounding Vṛndāvana, Lord Kṛṣṇa, by His silent response to Brahmā’s prayers, indicated that Brahmā should return to his own abode. First Brahmā had to complete his personal devotional service of universal creation; then he could come to Vṛndāvana and get the mercy of the inhabitants there. In other words, a devotee should always be attentive to executing his personal devotional service properly. This is more important than trying to live in the Lord’s abode.
Source:A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Tenth Canto, Chapter 14 – Text 41