I don't know.
I'm getting all of this from wikipedia so don't hold me to any of this.
Brahma is considered to be part of a trinity including Vishnu, and Shiva. Brahma is the creator aspect of God. Shiva destruction. Vishnu the ultimate onminpresent reality. Given the mystical approach that some Hindus like, maybe he is not so popular because Brahman (which is similar in name) represents the supreme universal spirit that supports reality. And Vishnu seems to share qualities with Brahman.
According to wikipedia, Vishnu and Shiva sects elevated the status of these two aspects of God between 1000 and 700 BC. Vishnu somehow became associated with the belief that he is the aspect that comes to earth in the form of Avatars to help liberate human beings from Samsura.
In the Judeo-Christian belief system, designating importance to the One God as a creator and controller of all that was, is, and will be became very important. In Hinduism, the need to believe that God controls all of history from beginning to end seems different. Ideas about "ultimate reality" and the mystical nature of existence itself may be the influence. The starting point of everything may not be the main concern. The emanation of all of reality from God seems more important. Mystical branches of Judaism (like Kabbalah) and Christianity (while gaining interest) haven't made it into popular culture to the extant that mysticism has in Hindu cultures.