Because of the fact that everyone loves Kate Middleton, and since she can do no wrong in the public eye, everyone is excited to see her become Queen Consort as soon as possible.
However, not only will it be at least 30 more years before she and Prince William take the throne since Queen Elizabeth is 93 and still going strong, and not to mention that the Queen could live longer since the Royal Family comes from excellent genes, everyone seems to forget the fact that Camilla Parker Bowles is next in line for Queen before Katecan be named this major title.