To be precise, the US does have life+70 for works published after 1978. The rest of the world went that route and the US begrudgingly followed, but the works published before the switchover date are grandfathered into the old system. The US copyright regime is a real rats' nest of complexity, see https://guides.library.cornell.edu/copyright/publicdomain
> The US copyright regime is a real rats' nest of complexity
The likely alternative would be (even more) retroactive copyright extensions which would be much worse.
Until they bribe the supremes to revise the ruling.