Why do academics hate Tolkien's Lord of the Rings?

When Lord of the Rings came out in 1954 Yale Professor Harold Bloom read the novel and he was not impressed, describing it as: “inflated, over-written, tendentious, and moralistic in the extreme." He further concluded that: "whether Tolkien is an author for the coming century seems to me open to some doubt."

Harold Bloom was not alone in his criticism. Many academics were scathing in their reviews of Lord of the Rings. But given how popular Lord of the Rings has become to the general public, why is this, why do academics hate Tolkien’s Lord of the Rings?