The steam explosion is based off two assumptions: You're starting with cold sausage that heats up as it coalesces into the star, and that the steam gets trapped by the solid mass of sausage above it. Stars normally coalesce out of hydrogen that doesn't need to go through as drastic of a change as a sausage would when transforming into fusing plasma. My assumptions are probably at least partially incorrect because my field of expertise is really ribs and brisket.