I think sometimes, to save space, they reduce the size of the puzzle.  One time, my wife got out a magnifying glass to work it.  It was a daily puzzle though, not the big Sunday one.

These young people don’t realize some of us are sight impaired.

Whomever is setting up the Sunday crossword is not trying hard enough. With a little more effort, it can be squeezed down to where you cannot write in the blocks, much less read the numbers. Remember, the elderly cannot see as well as you can.