He lives in an ivory tower and ignores real problems.
ivory tower
idiomA sheltered, overly-academic existence or perspective, implying a disconnection or lack of awareness of reality or practical considerations.
Origin
first recorded 20th c.Calque of French tour d'ivoire, based on a biblical phrase, coined by Charles Augustin Sainte-Beuve to compare the poet Alfred de Vigny (more isolated) with Victor Hugo (more socially engaged). First attested in English in a translation of Laughter by French philosopher Henri Bergson (1911). The term was popularized in The Ivory Tower (1917) by Henry James, though used in different sense (millionaires, not professors).
The professor's ideas sounded brilliant, but his colleagues felt he was stuck in an ivory tower, far from the needs of actual students.
By remaining within the safety of his ivory tower, the philosopher failed to grasp the urgent economic struggles facing the citizens outside his university walls.