Who says that Peter was a "pope"? The papacy is a historical. development. The wandering preacher's successors became also the successors to Caesar in Rome, as pontifix maximus, but that could change in the course of time. John Paul II deliberately put away the imperial trappings and his successors may even move away from the Vatican, for these are non-essentials. The appointment of bishops is likewise a historical devlopment. To keep the Church from becoming a toy of monarchs, like the Russian Church, the pope finally won the right to "rule" the church after a thousand year struggle with Catholic princes, ironically after he lost a thousand year battle to remain a territorial prince. But his relationship with the organizational church will undoubtedly change. although in unforeseeable ways. In answer to your question, why didn't Peter--the undoubted leader of the Twelve--appoint James?
Well, that wasn't Peter's job.You play, I guess, a much different role in the scheme of things than did the remote great-grandfather whose name you own, but you are his heir, nonetheless. No pope is a carbon copy of Peter, anymore than you are of your remote great-grandfather, with whom you probably do not even share DNA. The mapping of the human genome surprised all in showing how even biology is unpredictable. Over 75 generations. how different do human beings becomes, and how different their ways. Yet there are constant threads.