Why are van der Waals' forces between gas molecules strong near its critical temperature?
Critical temperature is  kind of measure of the strength of intermolecular van der Waals force.

Comparison of actual and critical temperature is kind of comparison of average kinetic energy of molecules with energy needed to break the intermolecular bonds.

So temperature itself does not say anything about the bonding strength. It only indirectly determine probability these bonds get broken by thermal molecular motion.