Indeed that is the most important aspect of car tires but traction is not a catalyst in the decision of making bumpers, rubber, therefore extraneous to this question.
Yes, but you said, "the same reason why cars have rubber wheels" not to mention, cars generally have plastic bumpers, so your answer was a bit out there...
yes there are multiple reasons why rubber is used on tires I listed those that are in relation to why they use rubber on bumpers. the issue was bumper cars not vehicles. please read the question before answering it.
Because of rubber's natural property of the reflection of kinetic energy in the form of recoil. With that, when two bumper cars collide, they really bump harder, otherwise they'd just smack into each other and sit there, crashed and broken.