I don't understand why they really did this.
You could say that because they are popular, they wanted them also in this new book so that people could combine them with the new material of this book, and play them thanks to the AL "+1 book" rule.
On the other hand this new book doesn't have THAT much player's crunch. There's many spells, but only the Storm Sorcerer will use them (in fact my original guess for SCAG reprints was Storm Sorcerer + Bladesinger Wizard + Arcana Cleric + Undying Warlock).
So basically the only reason why someone already having SCAG and playing a Sun Soul Monk or Mastermind Rogue would want to buy them again and choose XGE as her +1 book for AL is... the racial feats? :/