Yesterday, I come to a local glasses store for a pair of reading eyeglasses, the SPH is only +0.50, the optician told me that it's hard to fabricate the glasses for me with half rim frames, any one can tell me why this happens?

That's true, the edge of your lens will be very thin with such a low SPH as your prescription, it's difficult to cut the grooves along the edge of the lens, especially if you want a large frame, I suggest you should try rimless frame or choose a smaller one.Good luck!