Why does pre-frozen Kale/spinach loose 90% nutrition?

First of all, check your serving sizes. If they’re by volume, like, “1 cup”, then a serving of fresh, raw kale is going to be a considerably smaller amount of kale than 1 cup of frozen chopped kale. That stuff loses a lot of volume when frozen and then thawed. What you want is a weight based serving size, like 100g or something, if you’re going to directly compare nutrition data.