There are many important reasons for replacing traditional materials with plastic and/or rubber:

Cost effective alternative to traditional materials, such as metals and wood.
Less wear – Reduce & eliminate wear on mating surfaces
Higher performance – Plastics have outperformed other materials as much as 2 to 20 times. Lower coefficient of friction, reduced noise, reduced wear on mating surfaces, reduced electrical consumption, and steady bulk material flow
Less abrasion – Material formulated to handle various types of abrasion
Lower lubrication & maintenance – Can be eliminated or significantly reduced
Reduced impact & vibration – Eliminate structural damage due to shock, vibration, and impact
Corrosion resistant – Unaffected by most corrosive environments
Improved safety. Reduced injuries & claims – Lighter than metals, easier to move around and handle
Lighter weight – Easier handling and installation, and reduced shipping costs
Lower material costs, reduce downtime, lower maintenance costs
Reduced noise – Reduce/eliminate noise concerns
Aesthetics – Modern-looking shapes & colors

Redwood Redco - Model 20B, 26B, 28B, 220, 226, 326 - Hanger Bearings Datasheet