John says that many people from Judea have come to comfort Martha and Mary concerning their brother. Martha goes out to meet Jesus, while Mary initially remains in the house surrounded by mourners.
When Mary rises quickly, those consoling her follow because they assume she is going to the tomb to weep.
Jewish mourning was strongly communal. Family, neighbors, and friends visited the bereaved, shared lament, and accompanied them during the days following burial. The home became an important center of consolation, while visits to the tomb and expressions of grief were also natural. Later rabbinic customs provide additional detail, but John's own account already demonstrates the essential social pattern.
Bethany's proximity to Jerusalem helps explain the presence of numerous Judean visitors.
The background explains why Jesus' encounter with the sisters does not occur privately. Grief is being carried by a community.
It also has narrative consequences: many of the people who came merely to console the family become witnesses to the events at Lazarus' tomb, and their responses help drive the conflict that follows.