In the 19th century, before many urban areas lacked recreation areas, many people chose to have picnics, and other celebrations, in local cemeteries.
Unfortunately historians say one of the reason picnicking in cemeteries became so popular is because of epidemics like yellow fever racing across the country. Death was a constant to many families, and in cemeteries people could break bread, and "speak", with their family members.
Read more about this strange part of American History on Atlas Obscura.