That the chisel is 1″ should not make too much difference. True, more metal has to be removed than on a 1/2 inch chisel, but a lot less has to be removed than on a plane iron. And if the back is flat and polished, and the bevel on your chisel is already established (often 25 degrees to 30 degrees — though I never actually measure mine), not much metal has to come off to get the edge for it to be sharp.
Are you sharpening using Paul’s method? When I find I did not get a sharp edge, it is often because I simply did not sharpen all the way to the edge. I often take a quick look at the edge after the coarse stone to make sure the scratches are all the way to the edge and square across (to make sure I am not sharpening out of square). You should also be able to feel a burr, unless the course stone simply broke it off already, which I find happens. In any event, if after the medium stone, you still cannot feel a burr, you did not sharpen all the way to the edge. No burr, no sharp edge. It does not have to be large, but it must be there. That burr gets polished off on finer stones or, on Paul’s method, on the strop.
If you used your stones correctly, there is a second way you might get a poor edge. You might have a great edge and then round it off on the strop. You have to PULL the blade across the strop being careful not to raise the blade us so as to blunt the edge.
You mention a sanding belt. Are you just using that, laying flat on a benchtop or whatever, to flatten the back? Or are you doing some sort of power sharpening with the belt to establish the basic edge before turning to stones? That was not clear from your post.