They likely coded it all in quickly in a messy fashion that they didn't think about ways to disable any of the tracking in the EU and that's why is not available there at launch. While Meta has plenty of software engineers to get jobs like this done the speed they supposedly went to get it done(Being start in January launch in July) likely means things got rushed as it supposedly wasn't planned to launch till later this year but with twitter imploding Meta wants to get as much of the existing marketshare moved over quickly with instagram being the perfect way to make moving seem easy.