The reason Apple is still playing games with the EC is that they're waiting on an EU Court's ruling[1] on whether Article 6 (7), the provision that mandates free of charge iOS APIs for all developers, is "constitutional" within the EU framework itself.
Most people who call out the Core Technology Fee use that provision as one of their main arguments, and it's one of their strongest, because the "free of charge" language throws away the general idea that the law doesn't want to interfere with Apple's monetization strategies. Since Apple could very well have chosen to monetize certain local API access in the past, the fact that this provision put a stop to that effectively nullifies Apple's argument (to the courts) that the law could never have meant to actually control how they make money.
[1] https://curia.europa.eu/juris/fiche.jsf?id=T%3B1080%3B23%3BR...