Informants are often compensated in a variety of ways. Maybe you get some cash or maybe you avoid arrest or torture in exchange for giving up someone else. Or maybe becoming an informant was a criteria for government sponsorship in academics or sports or to keep their position in a high profile career. Although some informants just do it for ego or ideological reasons. Is your neighbor annoying you with their late night clandestine meetings? Rat them out! It's unfortunate that these records don't include reasons as to why someone became an informant and what information they actually contributed, if any.