Why would someone want to sync bookmarks, browsing history etc between their phone, their iPad and their computer?

Chrome and Firefox do the same.

Firefox only does this if you set it up that way. It's in no way obligatory. That is a far cry from Apple and Google.

And you can disable bookmark syncing for both Google and Safari.

But what privacy threat are you trying to avoid by not having your bookmarks and history synced in an E2E manner where Apple can’t see either?