They don't want people to know that they are there. They like to work by stealth. They want to be able to do their work of destruction without confrontation or challenge. It is when we recognize them and try to move against them, that they become most violent and troublesome. That is when they dig in their heals and refuse to leave.
Most Bible commentators spend time writing about demon possession as a spiritual or health problem.
Meyers reminds us that the possessed person was considered a social outcast. In Jesus' day religious leaders marginalized anyone who was sick. Lepers were sent to a leper colony. Women with a flow of blood were not to be in public. It was done, ostensibly, to protect others, to safeguard the ritual cleanliness of the people of Israel.