In a time-limited acute health crisis, an IC might choose to shelter these populations in place because:

In a large-scale evacuation, all available resources will be needed to evacuate the general public. The large volume of people requiring transportation will overwhelm buses and other means of transportation. These means of transportation will not be able to respond to the equipment and labor intensive requirements of special needs populations. Recognizing this, Incident Commanders may elect to shelter special needs populations in place while evacuating the surrounding population.