People complain all the time about how bad players are now so imagine that new players get to start at level 60 and skipping everything to that point. They wouldn't have done any job quests to give any type of basic understanding of how the job works, they would have 60 levels worth of abilities that they don't have half a clue how to use or what's going on. What equipment would they even start with? It would be a disaster. Would anyone want a day 1 level 60 tank in your group? Would they even know how to join a group? They would be completely lost.