Why in Superconducting State ($T < T_c$), Drift Velocity of Electrons is Low?

I was studying Hasan Padamsee's book about RF Superconductivity and I encountered a section in the superconducting essentials' chapter. Dr. Padamsee's intention is to prove why in superconducting state (i.e., $T<T_c$ ), metal impurities does not scatter Cooper pairs, causing resistivity. He says in a normal metals, electron velocity is very high and de Broglie wavelength is comparable to lattice dimentions. So disturbance in lattice structure (i.e., impurities) cause resistance. In case of a superconductor carrying current, all pairs drift with one and same velocity in the direction of the current (that's legit). When the current $\mathbf{j} = -n2e\Delta\mathbf{v}$ flows, it is carried by a large number of Cooper pairs so that the drift velocity of the individual pairs is very low. Therefore the wavelength is much larger than lattice dimensions and scattering by imperfection is impossible, leading to zero resistance. My question is how come the drift velocity of Cooper pairs is low? The passage I am referring to is from Hasan S. Padamsee's RF Superconductivity for Accelerators, Chapter 3, Section 3.4, “Electrical Properties, DC and RF Resistance”, p. 73.