It's the sad reality of not being a hub of any kind. We are close to several hubs so it's unlikely we will ever attain even regional hub status (Silver Airline's aspirations notwithstanding). On the flipside, as an underserved midsized market (in FL especially!) we are able to attract these LCCs. Not just the big expansions of Frontier and Allegiant, but even Southwest and Jetblue back in the day were fairly early to our airport.
Regarding San Juan, I heard differently. In any case, those flights were often dirt cheap I am sad I never got to take advantage. Certainly our PR connection is growing so it could return someday soon.