Ashutosh Jogalekar in The Curious Wavefunction:
Physics, unlike biology or geology, was not considered to be a historical science until now. Physicists have prided themselves on being able to derive the vast bulk of phenomena in the universe from first principles. Biology – and chemistry, as a matter of fact – are different. Chance and contingency play an important role in the evolution of chemical and biological phenomena, so beyond a point scientists in these disciplines have realized that it's pointless to ask questions about origins and first principles.
The overriding “fundamental law” in biology is that of evolution by natural selection. But while the law is fundamental on a macro scale, its details at a micro level don't lend themselves to real explanation in terms of origins. For instance the bacterial flagellum is a product of accident and time, a key structure involved in locomotion, feeding and flight that resulted from gene sharing, recombination and selective survival of certain species spread over billions of years. While one can speculate, it is impossible to know for certain all the details that led to the evolution of this marvelous molecular motor. Thus biologists have accepted history and accident as integral parts of their fundamental laws.
Physics was different until now. Almost everything in the universe could be explained in terms of fundamental laws like Einstein's theory of general relativity or the laws of quantum mechanics. If you wanted to explain the shape and structure of a galaxy you could seek the explanation in the precise motion of the various particles governed by the laws of gravity. If you wanted to explain why water is H20 and not H30 you could seek the explanation in the principles of quantum mechanics that in turn dictate the laws of chemical bonding.