When camera makers switched to autofocus they switched to making their screens brighter, especially with all those dim kit zoom lenses. A dim, but very focusable ground glass would not cut it any more since the kit lens was no longer a 50mm/F1.4. The very technology that allowed for brighter screens made them more difficult to focus. No stock screens in any autofocus camera are designed for manual focus. Use live view for that. Or get something like a Brightscreen that includes tools like microprisms and split images.