Only US carriers exclude lounge membership as a benefit of the top tier status. This is in part an historical matter, as US airlines were prohibited by the anti-discrimination laws of the 60s to give memberships free of charge as they had been doing for decades to their best customers. This led to the current situation of selling annual memberships (and also a less restrictive access policy, but that's another matter). Once this was established, lounges became a profit centre and giving memberships away even to top elites would become a costly proposition.

Foreign airlines had no such restriction and continued to offer free membership to their lounges as a sales promotional tool. When FF programs came along, this was extended into the top tier package of benefits, and thus most provide free memberships.

I noticed AA is promotionally offering Admiral Club memberships as an incentive to keep flying with them once a member has achieved their Gold or Platinum status for the year. But this is an exception.