Microsoft is here in 2021 as well. IBM, too. But they aren't the powers that they used to be.
Book selling is highly symbolic for Amazon, because they grew out of this niche. Also, banning books has a specific bad taste associated, because that is what authoritarians over the ages have done and liberal people resented such bans.
Bans are mostly local affairs. For a shop, if they refuse to carry a certain book, they have effectively banned it from their domain of power, which is what matters.
I know that they once removed 1984 from Kindles due to a copyright issue. Some people noticed even then. But a momentum of interest takes some time to build up. If Amazon starts expanding their blacklists frequently, it will attract more and more attention.
They've been doing it for quite a while; RMS pointed out that they retroactively removed 1984 from people's libraries nearly a decade ago. No regulator cared then, no regulator will care now.
Banning books isn't a particularly controversial thing; this isn't even banning them, it's just...not selling them.
