  We argue that the unusually strong electron-electron interactions in the
narrow bands in moir\'e superlattices originate from compact Wannier orbitals.
Enhanced overlaps of electronic wavefunctions, enabled by such orbitals, result
in a strong el-el superlattice umklapp scattering. We identify the umklapp
scattering processes as a source of the strong temperature-dependent
resistivity observed in these systems. In a simple model, the umklapp
scattering predicts a $T$-dependent resistivity that grows as $T^2$ and is
getting bigger as the Wannier orbital radius decreases. We quantify the
enhancement in el-el scattering by the Kadowaki-Woods (KW) ratio, a quantity
that is sensitive to umklapp scattering but, helpfully, insensitive to the
effects due to the high density of electronic states. Our analysis predicts
anomalously large KW ratio values that clearly indicate the importance of the
umklapp el-el processes and their impact on the $T$-dependent resistivity.
