Are you looking at non-stop flights? If so, you are probably looking too far out. About 30 days to six weeks is when the best fares seem to appear. I get the impression that ULCC passengers book later than your average airline customer. Either that or this is a prime travel period and Frontier thinks they can get people to pay the fare they are publishing. I would bet fares will lower as the travel date gets closer unless travel demand really is strong this summer. Either that or Frontier will cancel the flight