Rumors

A rumor starts with " I heard that..." and it is usually what someone does when they try to figure out the truth with other people from bits of facts and also fiction. Rumors spread and then die over time. Gossip, on the other hand is sharing information, which may be true, and it could be for entertainment or to bond with another person. Now that we have the difference, here are some possible reasons why people like to spread rumors:
Makes them feel superior
Some people feel bad about themselves, and spreading rumors makes them think that they are better, like it's ok for them to be near the bottom as long as they're not actually on the bottom. And for these people the easiest way is to make up a rumor that in their mind puts someone under them.
For attention
For these kind of people, a rumor is like money, if you spread it you buy the attention of whoever is up to listen to it, even if it's for a few minutes.
Jealousy or revenge
Jealous people make up rumors about someone in order to hurt them. Or if someone ever feels a person did something bad to them they might make up rumors to satisfy their need for justice.
Out of boredom
I saved this reason for the last, cause in most of the cases people make up rumors because their life is just too boring. A rumor might shake things up a bit, or get two people to start a fight, and that makes life seem interesting for these bored people.