The reasons for the gradual layout are not purely legal. But also technical, social and even psychological. Most bot farms are outside US and UK, but US and UK

The reasons for the gradual layout are not purely legal. But also technical, social and even psychological. Most bot farms are outside US and UK, but US and UK are the majority of popular users, and English-speaking audience, which is a key demographic for any social media, because most communication on social media is still in English and culture is biased heavily towards US/UK culture online. So starting the app there provides "anchoring" for the culture on the app. Also the app may have issues with complex mixed order writing systems and localization for all those additional countries, so following Paretto is great here, you get 80% of the target with 20% of the effort. Also scaling a new platform from 0 to 100 in an instant is just a rookie thing to do, and Meta ain't rookies.