Lots of medical equipment is plastic. Most outdoor clothes are plastic. Many parts in a car are plastic. Suitcases, bags, etc are plastic. Shoes. Bookbinders, covers, cases, just look around the place you are right now and you will notice more plastic the longer you look.
I see the following advantages:
- Onetime use disposable
- lightweight
- durable
- manufacture is easier and cheaper
- often the better solution than the previous one