Perhaps its because there are some people who actually believe that there are people who can be trusted. That not all people are out to take advantage of one another, that there may be some people who care for one another, give of themselves, their time, talents, and money. I think they believe things that are not true for this reason, they have trusted the untrustworthy.
It is unfortunate that anyone takes advantage of a gullible person especially knowing that they are gullible.
The bottom line is people, some people, gullible people believe that there is still some good in each of us.
I know that the only good thing in me is Jesus! Thank God that He is there! Thank God He changed me, if He could change me, and He did! He can change anybody!!!