Grayjay and other Futo apps are not really paid software, it’s more like a donation. No reason not to use a FOSS license.
But Grayjay can’t use the Blender model because the biggest player in the industry (Youtube) has a vested interest in keeping the app from being developed.
What does that have to do with the licensing? The restrictive definitely won’t stop Google from trying to shut the app down. Selling the app actually makes it harder to prevent it from being shut down. Google can now argue in court that Futo tries to make money from selling this app, that uses the YouTube API without authorization.
There’s a very easy solution to this problem: Just make it FOSS like every other god damn alternative YouTube client, put the GPL on it and treat donations like donations, instead of “selling” the app and generating revenue (which can and likely will be used against them).