Why do the most massive stars have lifespans measured only in millions of years?

They burn through hydrogen fuel supply the fastest

Despite possessing much larger reserves of hydrogen fuel than smaller stars like the Sun, the most massive stars burn through that supply at an exponentially accelerated rate, leading to surprisingly brief lifespans measured in millions of years. This rapid depletion stems directly from the necessity of generating colossal outward pressure to counteract their immense gravitational self-attraction, which is hundreds of times stronger than the Sun's. To achieve this required pressure balance, the cores of these massive stars must operate at drastically higher temperatures and densities than solar-like stars. This results in hydrogen fusion occurring at an astonishingly high rate, effectively consuming their fuel supply much faster than the comparatively leisurely pace seen in less massive stars, illustrating a key paradox of stellar economics.