The cost of legal propriety

Sarah Williams and Katrina Walsh were found guilty today of a heinous, pre-meditated crime of great ferocity and savagery. They murdered a sixty year old woman, Sadie Hartley, on the doorstep of her home, using first a stun gun and then a knife inflicting forty stab wounds on the victim.
The evidence against the two accused was said to be overwhelming so why then did the trial last seven weeks with all the attendant costs, not least the re-reimbursement of the jurors who had to sit through the details of this harrowing crime.
The public purse will now have to keep these women behind bars for many years at an estimated £400 per day each, but what of the trial itself. The women, presumably pleaded not guilty but on whose advice. Surely their lawyers would have advised that acquittal was impossible. Is there no provision in law for the judge to say that such a plea is unreasonable given the evidence thereby denying the accused their day in court to air their grievances and delight at their deeds. Were there mitigating circumstances, were the accused mentally unbalanced? I don't know but it strikes me that this trial demonstrates yet again why the public money grabbing legal profession, for all its claims to be the world best, needs to be trimmed. The cost of justice is unaffordable if obvious guilt is allowed to be set aside in favour of long trials with jurors. Jurisprudence is one thing; common sense is another.