They're very cautiously dipping their toe in the water given the holy shitstorm that happened a couple years ago when they announced they were going to block third party cookies by default. I imagine that doing it this way means they can show metrics that blocking in this way doesn't meaningfully affect bottom lines.
Safari doesn't. They advertise that they do but the policy is riddled with heuristic exemptions added in as they tried to fix broken websites. This (IMO dishonest) behaviour is what led to the Murdoch-driven blowup about Google and ad tracking a few years ago - Google was using one of these workarounds when the user had opted in to ad tracking and it ended up disabling more of the safari cookie blocking logic than they expected. This undocumented behaviour then became Google's fault somehow, although really Safari was just not doing what it claimed it would do.
