  Recent gravitational microlensing observations predict a vast population of
free-floating giant planets that outnumbers main sequence stars almost twofold.
A frequently-invoked mechanism for generating this population is a dynamical
instability that incites planet-planet scattering and the ejection of one or
more planets in isolated main sequence planetary systems. Here, we demonstrate
that this process alone probably cannot represent the sole source of these
galactic wanderers. By using straightforward quantitative arguments and N-body
simulations, we argue that the observed number of exoplanets exceeds the
plausible number of ejected planets per system from scattering. Thus, other
potential sources of free-floaters, such as planetary stripping in stellar
clusters and post-main-sequence ejection, must be considered.
