The belief in one Supreme Being, which for many is a personal God (brahman) is a vital part of Hinduism which you should take care not to forget. The various “gods” of the Hindu pantheon are ultimately manifestations of the one divine reality. Christianity itself is accused, especially by Muslims, for being polytheistic (e.g. the Trinity). God in the Old Testament goes by many names (Elohim, Yaweh, El Shaddai etc.), and Christians across the globe have a varying understanding of who God is. Moreover, Hinduism is very much a culture as well as a religion (sometimes just a culture) - why would a Hindu, surrounded by Hindus, taught to be Hindu, suddenly decide to conform to a foreign tradition?
You may want to research the term “Bhakti,” and focus on it as it occurs at the highest level (look into the Bhagavata Purana and you’ll find some startling answers to your question)