Hi, I have a question. Why is that back line "out" in a doubles match and considered "in" a singles match which needs more footwork? This doesn't make any sense! (Three emotions in the question!)
I think that it's to do with 'Attack'. 1. Single is more stategic game than attack. 2. As we know, the double is a attack game, not like single. 3. In the double, the court is wider. 4. Give the receiver a chance to attack, so the game get more attractive. If you see the double match, the receiver does always a smash when he gets a high service.
That's the rule. Singles coverage is already narrow and long without the tramlines areas. Doubles service is short and wide.
If the back line were "in" on service, then attacking the serve in doubles would be much more difficult.
Because in doubles, you have two people defending a smash so it's easier to return a fast smash. It's not much of a problem that the reciever is smashing a high serve. In singles, it's a lot harder since one person has to defend much more area. Thus we equalize the weakened defense but weakening the offense by forcing the attacker further back. Otherwise, the singles game could end a lot quicker than it does now.