Why cant people who committed suicide be buried in church cemeteries?

Most likely because suicide is considered self murder. Also that some foolish self appointed Gods of the non compassionate religion thought that they were doing God's will.

Suicide is a sin if the persons mind is sound at the time of the act, but who really knows why a person kills themselves?. Most are committed because the mind of the person is not stable at the time. What right has anyone to say that they cannot be given a proper burial in a church yard. Has any religion the right to judge a person who commits such an act. Let God be the judge, and give the unfortunate a proper burial.