Because it might not have been the “Spanish”, but certain people who ruined history. So it’s not fair to blame a whole country for the actions of a few.
It's pretty fair to blame the entire social and political system of 16th century Spain, which at that time was centered on religious persecution, mass murder, large-scale theft and exploitation, and quasi-slavery, leading to centuries of profoundly racist tyranny in the Americas. The book-burning cultural genocide was just the cherry on top.
(As is common for feudal occupiers of foreign lands, and by no means unique to Spain) the worst kinds of psychopaths were continually elevated to positions of authority and then granted almost complete impunity to do what they wanted, with an ideology that treated the recipients of their exploitation as sub-human.
Duh. But not all Romans!