FalseP one of the problems is that QM is a linear theory whilst GR is non-linear. GR does describe the curvature of space-time geometrically dealing with rather large masses. QM does deal with the terribly small; subatomic particles usually. The first attack when you are trying to solve a GR problem is to see if you can turn it into a Special Relativity problem, wherein you are back to linear solutions. Non-linear problems are notoriously difficult.
String theory, loops theory and a few others are the contenders for the fusion of GR and QM.
We may never know however what causes gravity or the other three forces. Allow me to relay something Richard Feyman said which is true and in a way somewhat sad for scientists. Paraphrasing, he stated that eventually there will be some basic laws, perhaps the four we have now, perhaps something deeper. When you reach that point, the most basic rules of the universe, ultimately all we will be able to say is, these are the laws and they work the way they do. We will not be able to say why.