Completely agree. FR24, along with FlightAware, Radarbox24 and Plane Finder has built a business of monetizing free, crowdsourced data. For FR24 there's been multiple requests by the community to for an API, some willing to pay, but they've refused every time. I don't understand why people are eager to feed into those closed network.
ADSB Exchange on the other hand is built with an open premise, runs off donations, and encourages third-party app and value add to build off their API.
Well, we can do both. FlightAware has nice tutorials and client software for setting up an ADSB feeder on a Raspberry Pi, but I feed to ADSB Exchange as well with minimal extra effort.
They also started out with a fairly expensive premium app, and then jettisoned it in favor of a subscription-based service, leaving everyone who bought the app high and dry.
There's probably not much stopping FR24 from feeding off of ADSB Exchange. This happens in the weather world, where data from community-managed CWOP weather stations ends up in the hands of commercial weather data services, who normalize the feeds and incorporate them into their forecasting products.
That gets into the very tricky idea of "What is commercialization?" If you use a Creative Commons works that's BY-NC on your blog, but your blog runs ads, is it now commercial? What if it's funded by Patreon? That's why Wikipedia doesn't allow NC and the premise behind the Free Culture licenses.
ADSB Exchange on the other hand is built with an open premise, runs off donations, and encourages third-party app and value add to build off their API.