The major reason is that children don't always have time to take care of their parents. It is difficult for them to juggle working hours and still being able to attend to their parents. Another reason could be that people are generally reluctant to live with elderly parents as there is the generation gap, which could cause many conflicts, and, also, parents might require medical assistance as they get older. Therefore, it is easier to pay for professional care in a nursing home. I hope this helps!