I suspect also that, like JetBlue in its early years, a lot of its flights were out of secondary airports that are generally less exposed to a lot of operational disruptions. (e.g. they flew in Hobby in Houston early on). They also had the advantage of being in a region that's its name that probably has fewer weather issues in general.

The pattern I've seen over the years is that upstart airlines, as they grow, end up having to look--for various reasons--a lot more like legacy carriers over time. Whether that's flying into areas with seasonal bad weather, flying out of default airports, instituting various forms of passenger status, etc.