70 years is way too much. It should be something like 10 years. The idea is to give creators appropriate reward and then release works into the public domain. 10 years is more than enough time to make a fortune off of one's creations. They should have to invent
new stuff if they want more money.
What happens today is creators want to strike gold once and then enjoy a lifetime of royalties for themselves and their children. When was the last time something entered the public domain? Probably in the early 20th century. Public domain might as well be a forgotten footnote of history. There's no reason for the public to recognize copyright as legitimate when it's being systematically robbed of its rights.
What if the copyright is owned by a company? I don't know. Do they have to go bankrupt for the 70 year count to start? In any case, they'll probably just lobby for even more extensions before their terms run out anyway.