I can't stand paper sizes. The size of a sensor is approximately 36mm x 24mm with some variation usually within .1mm, but let's make it easy. For years the "standard" sizes were 3.5 x 5, 4x6, 8x10, 11x17, 16x20 etc. However the film format ratio was 36mm x 24mm or 1.5, so those 8x10 were cropped from 8x12. I don't know why we don't match the paper ratio to the size ratio except for 35mm isn't the only format, but it certainly was always the most ubiquitous.
The problem is if you want to use standard (CHEAP) frames, mats, etc. then you have to use what they make and the manufacturers don't use the 35mm ratio of 1.5.