They wouldn't, but until recently they provided explicit functionality that allowed apps to access a persistent identifier so advertising SDKs in those apps cou

They wouldn't, but until recently they provided explicit functionality that allowed apps to access a persistent identifier so advertising SDKs in those apps could link activities happening in between apps, something that's not normally possible due to app sandboxing. Now they've made that identifier explicitly opt-in (it prompts the user on first run) so if the user declines, advertisers have to fall back on probabilistic methods such as heuristics to try and link sessions together (which is harder especially if other countermeasures such as anti-fingerprinting, IP anonymisation with Private Relay, etc are used).