[dx034]

Not very scientific, but isn't it just laziness? Most people (including me) are too lazy to think about all the choices they could make, so they just stay with the default choice most of the time. Not because they actually prefer it, mainly because they never even read it.

[runarberg]

Indeed. Your alternative theory doesn’t require an extra construct, and instead uses a pretty established cognitive behavior (the tendency of inaction) to explain the same phenomenon. I would say your explanation has the advantage of Occam’s razor, whereas Nudge Theory doesn’t.