Safari by default has a stricter storage access policy by default for all third-party domains, which requires you to visit the domain as a first party first. So it's probably that rather than ITP.
I have a general question if you don't mind. I use Firefox Beta. Why is Firefox going the route of a manual blacklist (disconnect) instead of working on some kind of programmatic machine-learning/somewhat intelligent third-party storage blocking by default that doesn't discriminate known against unnkwon trackers?