Life harnessing new resources is the most constructive way to compete.
Creatures that expand, expand exponentially.
Creatures that don’t, collapse exponentially.
It takes a minuscule percentage of a population to be expanders, for the whole population to quickly become expanders.
It would take an exceptional explanation to explain why creatures that could expand, don’t.
An exceptional explanation on par with explaining how a balloon could be popped in a vacuum, but the compressed air inside somehow remained in place instead of dispersing.
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Also - starlight is going unused on a galactic scale. Actively managing energy production will enable a larger, longer, and more efficient future.