In the field, you need to have a very high ratio of faculty to students. One faculty for each 8 students would not be unusual. Field trips are hard to schedule. They are usually done on weekends, but this conflicts with student employment. Outdoors activities are not determined by the best time to go, but when they can be scheduled.
Transportation can be difficult and expensive.
Overall, field ecology is often a difficult experience for both the student and the instructor. On the other hand, students are interested in what is happening to the environment. They are concerned about the extinction of species. The redesign of this course follows a completely different approach. Students visit a convenient field site either at their convenience or when some critical event is taking place.