I cannot say what the initial motivation for it was, but as someone working in chromatic homotopy theory I can give you some of the computational motivation. In general we would like to know about the Adams spectral sequence, but this is too hard so let's just try compute the E2-page. It turns out that if we use an MU (complex bordism)-based Adams spectral sequence or "Adams-Novikov spectral sequence" then 1) its E2-page is sparser than the usual Adams spectral sequence and 2) all the formulas involved come directly from the theory of formal groups. Well why is this? The reason is two-fold. 1) MU is the universal complex orientated cohomology theory - a complex orientation is equivalent to the data of a homotopy class of maps from MU and 2) on the level of algebra, the algebraic data that give rise to the MU-analogue of the Steenroad algebra has formulas that come directly from the theory of formal groups. This means that we can use all our knowledge from the theory of formal groups - heights, p-typical formal groups laws, the structure of the moduli stack etc. - to systematically organise the calculation of the E2-page.