What is the primary reason for the comet moth's very brief adult lifespan?

Answer

It emerges lacking functional mouthparts and cannot eat

Like many large silkmoths in their final stage, the comet moth cannot feed upon emerging, relying entirely on energy accumulated during its larval stage, which dictates a lifespan of only a few days to about a week.

What is the primary reason for the comet moth's very brief adult lifespan?
nameanimalinsectmothcomet