Like it or not, being signed in everywhere with iCloud is an amazing experience. I know this because I recently tried a second user account on my Mac that wasn't signed in to my iCloud account. It was jarring.
As an Apple user I take it for granted that my watch unlocks my computer. That text copied to the clipboard on any device is immediately, invisibly available on the others. That all of my contacts and messages are just there. That my Safari history and state synchronises.
You can't 'selfhost' this stuff. You may not like Apple -- I'm not trying to convince you -- but the fact is that there are a ton of benefits that their integrated ecosystem delivers that you just can't emulate yourself.