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AT&T (the ISP's) allocations are to AT&T Corp, not AT&T Services.

AT&T's 12/8 is used for end-user address assignments by AT&T Services. See https://bgp.he.net/AS7018#_prefixes for their announcements.

Most of their broadband subs are from legacy SBC (ameritech, swbell, nvbell, pacbell, snet). They got all their allocations separately. None of them came out of 12/8 or 32/8 traditionally.

Apple and USPS are not ISPs. It doesn't seem like they need a /8 though.

Comically when Apple would setup a store they'd ask their isps to provide an allocation rather than dip into their allocation.

From a global routing perspective this makes sense. Otherwise every store has to advertise its netblock on BGP. Not impossible, but it bloats the routing table unnecessarily. Better for Apple to keep those addresses on its campus and let the stores connect like regular Internet endpoints.

Even better would be for Apple to return most of those addresses and only use a handful of /16s for its hosted services like any other business and switch the internal nets to RFC1918.