Behavioral Economics falls prey to the same kinds of over simplifications it was a reaction to in regular economics. There are useful insights to be gained from both over simplifications but it's also good to remain aware of their flaws. To over simplify myself, traditional economics starts from the assumption that people are rational and then tends to over simplify the way they reason and the models of the world they reason about; behavioral economics questions whether people are rational and 'demonstrates' they are not compared to over simplified models of the world they reason about.

A simple example is the "default choice" effect. The standard explanation is that people are too lazy to check a box. A more sophisticated explanation would be that people infer information from the default they are presented with and allow it to influence their decision based on their assumption that the form creator is well informed and looking out for their interests. There is in general an under appreciation in behavioral economics that people are likely being more rational than the over simplified models they are benchmarking them against. There are lots of examples of this in the most widely known results.

I think a "good" behavioral economist would not explain exactly why, but instead provide theories with as much data to describe why those theories exist.

A trial shows that people often exhibit behavior A. Why they exhibit behavior A may be complicated.

In your example, there's a sense of authority and conforming to a norm that can be used to describe those behaviors. But there's also the cognitive barrier (which we call lazy) that requires someone to exert mental effort to change away from a default.

It's not that one is wrong and the other is right. All of these may be right. But B.E.'s best contribution to society isn't to explain so much of _why_ we act in these ways - but instead to accept that despite our desires or perspectives of rationality, we do act in these ways.

Understanding the "why" may help us to make better decisions, certainly; however, being too prescriptive about "why" may lead us down the wrong path.

The way that behavioral economics is very often presented is not with the epistemic humility you describe here however. This is in part the fault of media popularizers and entities that use behavioral economics to justify and push their own agendas but in my experience the well known names in research are also culpable, both in their own popularizations and applications of their research and in their academic work.

There is an admirable strain in classical economics of epistemic humility: assuming that when human agents act in the world in ways that don't appear to match economic theory, it is at least as likely that the agents are acting in their own best interests and the economic theory, model or data are wrong than the reverse.

Behavioral economics tends to follow a less admirable strain of economic thought that assumes when agents don't follow the predictions of our over simplified model, it is the agents who are wrong and not the model. This is merely misguided in it's benign form but becomes pernicious when it is inevitably extended to "fixing" the agent's behavior through some form of coercion.

My criticism of BE is when it makes too strong a claim to agents acting irrationally rather than questioning where its own assumptions or models may be incomplete.

I find it somewhat useful if overly simplistic as an aid to analyzing and improving my own decisions. I dislike its use as another tool to justify telling people what to do. I also find its lack of introspection into its own flaws and limitations as a field disappointing.

It's similar to the classic spherical cows in many physics experiments.