Viscosity is the difference. Hagen-Poisseuille thinks of the fluid as concentric cylinders dragging on one another with drag being proportional to the contact area and the relative speed.
Motion of elecrons is not usually like this. Electrons move as diffracting waves scattering from imperfections of the material lattice, their kinetic energy being partly absorbed by the lattice. This absorption is what gives rise to ohmic resistance. Electrons don't normally drag on one another like the fluid, so the conductance of an ohmic conductor is proportional to the cross sectional area. If you double this area, you double the possible paths.
Electrons in some materials do indeed behave like viscous fluids. There have to be quite unusual correlations and conditions for this to happen, but it can nonetheless. Electron viscosity is a fairly active, recent research topic.