Another possible reason to consider, is at lv 11, 12 and 13, you break into some of the 'end game' gear, that when equipped at these levels can supercharge your effectivness, so much so that you can easily solo stuff at your level.

One example is greensteel items, and raid loot from titan/dq, and 2 levels after more from hox/vod. All this stuff on a tr turns a 'grind' into a 'sleepfest'

Before u equip this stuff you might need or even want to group, but after u can fly though quests so quick, that waiting for someone to join can only slow you down.