DSLR APS-C Sensors why are not converted to full frame?

Here is a dumb question, I put side by side my Canon 7D Mark II next to my iPhone 5S and I'm wondering why the iPhone camera the frame is larger (kinda like a full frame DSLR) than my Mark II. Why the APS-C Sensors are cropped and not just full frame like the iPhone? I think a lot of people would be more happy with if it was like that. Probably because of image quality of course but at least why they don't make it Feature on a DSLR On Full frame look OFF Full frame? I would use that feature all the time. That would be a great add-on of course the image would not be as good but if I had an on and off frame option so I can see more in my photo thumbs up i'd switch my Canon right now if I could get one with a feature like that. For certain things I use my iPhone because the dimensions are larger I can see more in a picture.

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