I think you mean barristers.

The problem here was that as many sub-postmasters were co owned by a husband and wife with children. There was an enormous incentive for one of the sub post masters to plead guilty and say, "my wife had nothing to do with it." Doubly so as the sentences would often be on the cusp of the "suspendible range", a guilty plea combined with contrition is much more likely to get a judge to suspend your sentence if he can.

Of course, this "plea-bargaining" is standard practice in the states but we aren't used to it in the UK.

The issue is that no barrister would allow their client to plead guilty without giving them a little canned speech about not pleading guilty if they didn't do it and having them, "sign their brief".