Huh?
ou technically have an automatic copyright in anything you write, if what you write is original and creative enough. Most people are not all that creative and original when writing, however.
If what is created is not original and creative enough to warrant registration with the copyright office prior to or shortly after infringement (and registration is necessary before an infringement suit can be filed), there are no statutory damages available to the copyright holder (and it will be the statutory damages that often make an infringement suit worth the high cost of pursuing).
Without statutory damages available in an infringement action, you must prove you have suffered actual damages (provable economic losses) or prove that profits have been made by the infringer when using your work. These profit/loss damages, if awarded, can be nominal at best.
So, if someone's creative or original works or words are purloined and copied or passed on to others or published online, there is often no reason for the creator of the work or words to sue over the infringement. The costs of pursuing such an action (even the cost of registering the works/words) can far outweigh any benefits realized.