The committee probably observed that in most cases where people wanted a move constructor, they needed either no copy constructor or a more complicated one (to handle duplicating a resource.) So creating a default copy constructor (a convenience in the common case of a simple structure) wasn't a win.

Perhaps if you were designing C++ from scratch without legacy and had a more Python-like mindset, you'd require an explicit "= default" rather than complicated rules about whether a default is provided for you or not.