There've always been solid human arguments for sustaining copyright legally. The balance is the tricky part.
On one hand we had a period where terms got too long, and some of the really aggressive legal enforcement from 20 years ago before stakeholders actually figured out how to get into digital markets were was entitled and useless. The pendulum also swung the other way with things like buffet streaming services essentially offering an economic bargain for creators with a sliver of compensatory difference from piracy but with none of piracy's actual benefits (people who simply pirate know they're not participating in a relationship of economic support with creators and might be persuaded to, someone who uses Spotify is under the illusion there's something fully legit on that front).
But the fundamental copyright bargain -- creators can recoup investments of time and effort in proportion to how popular engagement with their work is -- has always made sense.
> "We" now want stricter copyright law when it comes to AI, but at the same time shorter copyright duration...
Both these things can be true:
(1) Using a work as training data for AI is a very novel use, it's entirely plausible there should be novel considerations and rights to go with it.
(2) The incentive & benefits of copyrights have diminishing returns the longer the horizons are, while the cost in terms of social inaccessibility only increase. Where that's balanced out precisely is a debatable question, but something longer than a human lifespan is probably on the wrong side.