Because plastic is versatile, lightweight, flexible, moisture resistant, durable, relatively inexpensive, energy saving, and sometimes recyclable. It can be chemical resistant, clear or opaque, and practically unbreakable. Life w/o plastic is NO good life at all
Probably because of these points...
- Plastic is water-tight, and water-proof
- It's durable (it's not going to rot for a long, long time)
- It's cheap to make things from it once you've got the factory set up
- You can make it into any shape you want
- It's light
- It's an electrical insulator
- There are types of plastic that can withstand a lot of heat
- You can make it transparent
- You can reuse much of it