The court is concerned that it has been sentencing people to death (and carrying out those sentences) based on false information. This is the conflict facing Danforth and the court and this is the reason that they are biased against Marry Warren's testimony.
If they accept Mary Warren's version of events, they will also have to admit to wrongful killing, severely diminishing the authority and sense of justice entrusted to the the court.
At the heart of Mary's retraction is her terror at being hanged for witchcraft. Abigail is a very powerful character, capable of telling any lie to serve her purpose.
"Mary witnessed many sentences of death by hanging. When Abby turns against her and accuses her of sending her spirit out, she knows what will become of her."
When Abigail turns on Mary, she is at risk. Mary becomes so terrified about the prospect of her execution, she takes back everything she has said and accuses John Proctor of being in league with the devil.
The girls will say anything to divert the attention away from their behavior which has started this whole sequence of accusations.
Mary retracts her truthful statement because she does not want to die. She does not care if someone else dies, she will make up any lie to save her life.
Abigail is a dangerous character. She has no moral core, is unable to accept responsibility for that which she has done wrong and is selfish and self-serving. She enjoys the attention that she is getting, the chance to be emotional and wild, something that Puritanism does not allow.
The conflict at court with Mary and the other girls is simply peer pressure and fear. Mary Warren, like all teenaged girls, simply wants to fit in and be liked. No one wants to be the outcast or the butt of horrible jokes...it's hurtful and lonely. Mary runs that risk when she stands alone to tell the adults in the community that the girls are lying. Suddenly, Abigail, the ringleader, and the other girls who follow her lead, see a yellow bird in the rafters of the court. They start screaming for Mary not to let her spirit come after them to take it back. Mary's not very convincing when she tells them she has not let her spirit out and that there is no bird there. The adults can not see the bird, but they seem to believe the girls...excpect for John Proctor. Mary would rather face his wrath and the possibility of being fired from the Proctors' service than to be an outcast among the teen girls of the town. So, she run over to Abigail crying and apologizing, knowing that if Abby receives her, so will the others.