The main challenge with simulation is cost. Most actors are usually paid about $50/hour. There are also administrative challenges in terms of finding, training and paying actors. A full-fledged simulation program requires some infrastructure to ensure sustainability.
Another challenge with simulation is it tends to create anxiety for students given the unpredictable nature of the interaction. Educators often need to do extra emotional labour with students to help them through the exercise and to debrief with them afterwards.