  The lifetime of nonreactive ultracold bialkali gases was conjectured to be
limited by sticky collisions amplifying three-body loss. We show that the
sticking times were previously overestimated and do not support this
hypothesis. We find that electronic excitation of NaK+NaK collision complexes
by the trapping laser leads to the experimentally observed two-body loss. We
calculate the excitation rate with a quasiclassical, statistical model
employing ab initio potentials and transition dipole moments. Using longer
laser wavelengths or repulsive box potentials may suppress the losses.
