One can argue that the Internet Archive would be effectively useless if they strictly followed copyright law.
And I've only got a little bit of time in this life; I'd much rather read a trashy romance novel that was written this year and meant to entertain me than the trashy romance with politics that make me cringe that my mom was reading 50 years ago.
This is why, for example, the Library of Congress doesn't just keep a copy of everything. It's not just a space constraints or storage costs issue; it's a signal-to-noise ratio issue. As Mark Crislip is fond of saying, when you mix apple pie and cow pie it doesn't make the cow pie better, it just makes the apple pie worse.
For any published book, the answer of whether it's worth preserving that text is a very solid yes. There's not that much of it, no benefit to filtering.
And do you think future historians won't be very interested in those politics?
On a long enough timescale, the value starts increasing again. C.f. graffiti from Pompeii, Akkadian bookkeping tablets, etc.
Or, from another POV, cultural artifacts we dig out from earth millennia after they were buried still preserve something valuable. An entity like IA should think past one lifetime.
There's a better chance of you winning every lottery on Earth twice in a row than copyright terms being shortened in this century.
in the last century, birth control became first legal and then almost universal, automobiles became common, britain quit india, colonialism ended in most of the world, totalitarianism was invented, an antisemitic dictator conquered a continent and wiped out many of the world's biggest jewish communities, nuclear weapons were invented, the new york times published an editorial claiming rockets wouldn't work in space, men walked on the moon, communism enveloped a third of the planet, rock stars were invented, the majority of the human population moved to cities, global warming was discovered, the ozone hole was discovered and then solved, most of europe was unified under a single government, computers were invented, turing was bullied to death by the uk government for being gay, gay marriage became legal, women got the vote in most countries, liberal democracy enveloped half the planet, alcohol was legalized in the us, most other recreational drugs were prohibited in most countries, and some other things happened too
the next century will probably be less predictable than the last one