This is because relatively little energy of thermal motion is needed to overcome the energy of van der Waals bonding.

The liquid and solid phases of He, which result from weak van der Waals "bonds", exist only at temperatures below 4.6 K.

Even at temperatures near absolute zero, solid He can only be produced at high pressures (29.6 atm at 1.76 K).

Van der Waals bonds in molecular solids and liquids are generally stronger with increasing size of the atoms and molecules involved.