Simunitions are used a lot for training at the higher levels,
While this may be true in some instances, in my experience simunitions are used at places with larger training budgets and airsoft is used at places with smaller training budgets.
When the agency I work at was deciding if it should use simunitions or airsoft, the deciding factor was cost. We can train twice, maybe even three times, as much with airsoft than with simunitions. In a strapped economy, the cheaper but relatively equally effective (for our purposes) option is king.