They had insufficient funds to go to trial. The costs of these sorts of high profile cases are astronomical. They spent $4m in legal fees to get as far as they did. They would have needed +$10m to last to trial. The government drowns their opponents in discovery and all manner of delaying tactics in order to drive up the costs of trial, all while dangling plea deals with lighter sentencing. If they had gone to trial and lost it would have likely been 25 years instead of 5.