Why did the Undisputed title unify back into the WWE title and the World Heavyweight title?

Because, it was to much of a hassle to have one guy, be on Raw one week and Smackdown later the same week. He would, most likely, have major jet lag, pretty much all the time, considering Raw is live, on Monday, and Smackdown is taped on Tueday and airs on Friday. Besides you can't have a storyline with the heavyweight Champ, if he's bouncing around and it wouldn't add up, on why the Champ is facing the #1 contender he faces. Each feud, you see, is a storyline, and the storyline tells you why the guys are fighting eachother. It doesn't make sense, if everyone but the Heavyweight Champ, has a storyline. The only way it would be undisputed, again, would be to unify Raw and Smackdown. The problem with unifying Raw and Smackdown is: less storylines, less wreslters, and you can miss one show and watch the next to see what you missed, so WWE would lose money in the long run. You need competition to keep fans interested, which is why the "Monday night Wars" made the biggest profit, for both WWE and WCW. TNA isn't big enough yet, to make a difference, so Raw and Smackdown will remain seperate. I personally hope it stays that way, both shows are great, in their own unique way, which is the reason, I watch both each and every week, never missing a show. Brock Lesnar signed with Smackdown while he was the Undisputed Champ so RAW needed a title.