How long does copyright last for things made by corporations?

Everything I've ever seen about copyright says life + 70 years in the US. In looking this up I've seen how works with multiple authors are handled where the 70 starts after the death of the last author.

But is that really how it works for say The Avengers End Game. In 100 years or whatever would I have to track down every single person listed on the credits of the movie and determine when they died? Can a movie studio make sure to hire some young healthy people thus ensuring their copyright for as long as possible?

It doesn't make any sense to me but I can't find anything about this type of thing on the internet.