I think my honda accord 2012 was crashed because that rear bumper feels like plastic i don't know?

Shouldnt it feel hard? I touched another accord 2009 and it the rear bumper felt hard, mines felt soft

Bumper fascias ( the outside cover ) are plastic. Like any other plastic exposed to weather and UV rays, it hardens over time.

This is not a desirable trait though. You want the cover to be soft so if you have a very minor impact, it will bend and bounce back. If the bumper is old and hardened, it can crack instead.