The favored approach is,unfortunately, rather tautoligical: IQ measures 'intelligence' so imperfections with real world correlations can be explained by the notion that real world tasks are diluted with factors that are irrelevant to what we want to call 'intelligence'. This is opposed to the highly viable, but painful, explanation that IQ tests just dont pick up on other factors that are critical to generative thinking. One of the most hoary ideas is that because of some positive manifold, predicting a common underlying feature, it must reflect 'intelligence'. Absurd and akin to saying that because height is positively correlated to performance in practically all sports, that height = athleticism (interestingly, height is about 80 percent genetic, like IQ). There is absolutely no reason to view intelligence rooted in a single factor, especially, in light of late developments in cognitive psychology with intuition/heuristic processes which mediate analytical thinking.
Being good at math requires an intuition for mathematical computation. Most of this is occurring sub-consciously where there is no limit on conscious processing as there is with IQ. In general, IQ is more suitable to forming relationships in small systems, but the pieces by which those relationships are drawn, is rooted in what is empirical. IQ correlates less with true math ability than developed intuition and pure experience.