STABed U-Turn serves no purpose other than making U-Turn more powerful, which doesn't help it Scout.
Making what is arguably the best scouting move more powerful Doesn't help it scout??!
Making U-Turn more powerful makes it more likely to be deemed worthy of a moveslot and therefore more likely to see use on its movesets. This Does help it scout as it encourages more people to keep U-Turn on the moveset and use this pokemon as a scout, its intended purpose. Having U-Turn do 1.5 times more damage means it will be used more.
STAB U-Turn also helps by combining the U-Turn and STAB moveslots. Many people will see U-Turn as a must on a scout, and STAB is always useful to have. Combining the two means you can have both in one moveslot and with so many different ways to scout, this needs all the moveslots it can get.
STABbed U-Turn is a huge benefit for the Ultimate Scout.