Spain was literally a fascist dictatorship until 1975. Maybe some things take a while to grow out of.
The trial is subject to European courts and even if they dont appeal (which they will most probably do), this ensures that they are not abandoned to the purportedly fascist judges. So at the end they will be overseen by the EU.
By the way, Spain is one of the EU countries with the least unfavorable rulings by both the EU Justice Court and the European Court of Human Rights so I think that speak volumes of the fascist remains of our justices.
By the way the whole trial is available for anyone to watch in youtube, and judge Marchena’s job conducting the trial is widely understood to have been impeccable.