Why do high-mass stars not achieve a lifespan proportional to their greater total hydrogen fuel supply?

The rate at which they burn that fuel overwhelms their larger supply, leading to short lives.

Although a massive star begins its life with a significantly larger reservoir of hydrogen fuel compared to a smaller star like the Sun, the relationship between mass and fuel consumption is not linear; it is highly exponential due to core physics. The extreme gravitational compression necessitates ultra-high core temperatures, which drastically accelerates the rate of nuclear reactions. This accelerated burning rate means that even though they have more fuel, they consume it so rapidly—often thousands of times faster than a G-type star—that their total time on the main sequence is compressed into a period measured in millions of years rather than billions or trillions.