The answer to your question is no. I am not a GR expert but I have studied the theory in mathematical detail and the underlying fact that gravitational effects are caused by mass-energy seems only to be known by experience i.e. it is not deduced mathematically (a priori) but only empirically (a posteori).Although Albert Einstein had explained the new picture of gravity through his theory of general relativity, by explaining that gravity is the warping of spacetime, did he explain why mass actually warps this fabric of spacetime?
Define "very fundamental level". Also don't forget that curved spacetime is just a mathematical model. You could just as well ask: Why does force change the velocity of a body. The answer is: Because force is a mathematical abstraction that was defined this way.Okay, but the question wasn't what creates gravity, the question was why does mass/energy cause spacetime to warp? On a very fundamental level.
Any problem in science or philosophy or anything else in life can be turned into an undending string of "why"s that eventually become unanswerable except to say "that's just the way it is". That may be unsettling to you, but it is a reality that you must deal with - scientists do and as a result, there is a limit to how far they will go with such questions. Eventually, they really are pointless. They don't add any value to scientific knowledge.Okay, but the question wasn't what creates gravity, the question was why does mass/energy cause spacetime to warp? On a very fundamental level.