Why is it that some games are so god damn demanding?

I don't know much about programming/graphic design and stuff like that, and I would just like a direct answer to my question.
What I mean by it is, like, I download Skyrim, right, and I set the graphics and everything to high, and I m running it with literally 0 frame rate drops and it looks like heaven, but then I download Dragon Age Inquisition, and I set all possible settings to as low as they can get, the resolution and everything to as low as it is possible, and I m running this game on minecraft graphics, I can t even see grass or the faces of characters or anything, but I don t mind that, the thing I mind is that even with all that, my PC still has to give everything it has to process 1 frame per hour.
I understand that Inq has a higher demand than TESV, and my PC shouldn t be able to support it, but I d just like to know, as stated in the question: WHY? What is it that s beating the crap out of my PC in games with higher demands, even if I butcher them down to minecraft graphics and details?

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