It's somewhat of an iffy proposition to assume that the reported DoT traffic numbers accurately describe the true number of people in a market. Here are reasons that the potential GSO-MCO market is much larger than the 35 or so passengers per day each way:

(1) At about 10 hours of driving, many people choose to drive rather than taking a relatively-high-fare connecting flight. Even with ample, cheap nonstop service GSO-MCO there are many families who will drive But Frontier's service will grab some of that market.

(2) Some people in the GSO catchment area choose to drive to RDU or CLT for nonstop, (possibly) cheap service. Again, some of them who check GSO first will find Frontier's flights attractive.

(3) Some people flying from the Greensboro area head to areas around Tampa, Daytona, Melbourne, etc, will fly nonstop into Orlando instead.

(4) The report of 35/day each way may be under-reported as some regional airlines don't report. So if someone is flying GSO-CLT-MCO, if the regional airline flying the GSO-CLT segment does not report, it may not show up in the stats. It's not clear if there is any undercount in GSO-MCO, but there may be because so many GSO-xxx-MCO flights involve a connection with a regional carrier.

The biggest of these four factors when it comes to Greensboro-Orlando is #1. Orlando is such a massive tourist destinatino that huge numbers of people have to be driving or using alternate airports. Frontier may well (or may not) get enough people to pick them over alternate means of getting to Orlando. But it's a far, far bigger pool than 35 people / day.