Because current theories are missing an essential concept?
Suppose, for example, that applied to the enigma in our time called dark energy, characterized as accelerating space. If current theories do not avail in accounting for dark energy (so called) then neither can efforts at insight using those theories however persistently and strenuously applied, avail. The astronomical observations were made in 1997 and 1998. A convincing theoretical account has not yet emerged in over twenty years. What is needed perhaps (I think this the case) is a bit of luck that connects something sort of known (metabolic scaling, black body radiation) to something that seems mysterious, dark energy. What is needed is noticing a pattern found terrestrially to a pattern found cosmologically. What is needed is a fortuitous event. Perhaps, 4/3 scaling?
Are there historical examples of luck in physics?