The FAA may have data for the entire country, but iFly kind of doesn't, and can't...at least while in flight.
iFly is primarily for use in flight. Yes, it has some internet-supplemented capabilities that are available when on the ground, but mostly those enable or enhance pre-flight planning. Things like internet-based weather radar and other wx products, online flight planning, etc. Traffic monitoring at distant airports doesn't directly help with flight planning.
In flight, traffic data is only available locally. You can receive traffic data from targets directly in your line of sight, if you have a compatible-frequency receiver. Or, you can receive traffic data from an FAA broadcast, which will only include traffic within 15 miles laterally and 1750 feet vertically of your position (or maybe a little outside of that, if you happen to sniff out an ADSB transmission triggered by another nearby plane). But traffic data at airports more distant than 15 miles will not be available in-air (I'm assuming in-flight internet access isn't available, because it's iffy and can't be relied upon).
So, iFly would only have access to broader traffic data when connected to the internet, which generally translates to on the ground, when it's not needed to serve iFly's purpose.
As you point out, if you're on the ground or otherwise have internet access, there are already tools like FlightAware that can be used for flight tracking (or specific-airport tracking) more effectively than iFly.