There are several reasons to lead you to buy a pet stroller for your big dog. One reason is that your big dog is older and less mobile. Although these dogs still need their exercise, they may only be able to run or walk short distances before needing a break.
A second reason is an injury to your big dog. This is surely a temporary set back, but a pet stroller can be part of the rehabilitation program for your dog. Enjoying the outdoors is a much better option than lying in the house for 6-8 weeks.
A third reason is that you, the owner, are getting older, have an injury, or had surgery. Walking your big dog on a leash might not be feasible for long periods and a pet stroller will ease the strain.
Dogs enjoy the outdoor experience, and there is nothing better than spending time outside as long as possible. A pet stroller will give your big dog a break, or you, while you keep on moving.