Subconscious suspicion is one possibility; evolution only cares about your behavior, not so much about how much introspection you did to get there.

It's certainly not the only possibility, though. Another example: Reduce the bet to 55 cents vs 50 cents and I'd imagine refusing it myself, for the obvious reason that the expected gain is grossly less than the transaction costs of stopping to think about the bet, look for possible "catches", flip the coin, and collect any winnings. There's probably other rational reasons to be "bet averse" that I haven't thought of, too.