Watch for example last year's parade at youtube and you'll understand that your remark is just stupid. Half of Red Square is occupied by music band (last year it was more than a thousand military musicians from more that 15 countries). The other half is for marching troops. There is not much place for the guests left. Red Square is rather small - they didn't plan huge squares in middle ages somehow. Besides, most of the guests are veterans from all over Russia and other countries. I think it's fair. People who like to watch this live and not on TV are standing at nearby streets.