[magduf]

There is a certain cost to it.

Just like a reserve army full of reservists has a serious cost (those people all have to spend weekends training, after all: time that could be spent doing other things), a "health care army" would require people to get regular training to stay up-to-date and in practice. Basic first aid can be useful for anyone, but for having people ready to jump in and become healthcare workers in a crisis, they need a lot more than a first aid refresher once a year I think.