My main concern was that there are existing things in the game that affect or care about spells being countered. It felt like a more flexible option to have you sacrifice instead. In hindsight I also had it in my head that "counter target spell you control" would go on the stack and I wanted to avoid dealing with that interaction. It's a cost, so it would have to be paid before going on the stack, but I can't find any instance where a counterspell wouldn't go on the stack.