A lot of reasons. First of all, you can't skip it if you are playing Horde, Silverpine Forest is unfinished and you will run out of relevant quests by the time you hit 15ish, forcing you to go to the Barrens either way. Second of all, it has quests for like 20 levels and you have to periodically come back to pick up 2-3 quests which you couldn't before. It wouldn't be so bad if the zone didn't have so much walking around in a featureless savanna. And last but not least, the quests themselves have spread out objectives and are boring in general, too many "exterminate the local wildlife and native populations" type of deal. I think it exemplifies the fact that Horde zones were made last, too many levels crammed into a single *unskippable* gigantic zone without much variation. Barrens chat is cancer. The cherry on top is that the Alliance zones for the relevant levels are much better designed and varied, they don't force you to go anywhere and you have actual choices of where to level. Horde leveling in general is very linear, not only the Barrens, it's just the worst example.