Complexity costs of decision making is actually at the core of behavior economics, for instance one of the biggest insights (which sounds really obvious in hind

Complexity costs of decision making is actually at the core of behavior economics, for instance one of the biggest insights (which sounds really obvious in hindsight) is that people stick to the defaults. You can see this insight everywhere from opt-out dark patterns and default opt-in organ donor systems but according to classical economics something being default opt-in or default opt-out shouldn't matter because people will take the time to make a most optimal decision possible with all possible information. Most of the talk of 'rational' vs 'irrational' is because it is in opposition to the classical economics assumptions that people act perfectly rational with perfect information. The more full explanation a behavioral economist would probably give you would be something about how the human mind is optimized for a very different environment and takes short cuts appropriate to that environment that are not helpful in the current environment.