Only trademarks must be defended, or they are considered to have fallen into disuse, and cease to be the "property" of an entity.
So if Samsung found someone using a misleadingly similar logo, they would have to take action, or risk losing their trademark.
Patents are a 20 year (I think) period of exclusivity. And no matter how many people are infringing, one offender can still be singled out and brought to court. The patent holder must choose to sue, but they are not obliged to.
Same with copyright. No matter how many people infringe, the copyright period doesn't change at all. If it was otherwise, pretty much every movie, every song, and every big of software would be out of copyright, due to being copied by so many people.