If you are refering to the downtime right now, it's daily on US, Xbox & switch at this time. Game will be back momentarily.
No, server reset is at this time at most it's only ever an hour. Downtime (if intended) is always announced, in some post/tweet/form
Yep. The daily reset was instituted in the first year of the game, to help prevent the memory leaks the game has with terminating completed instances. The problem was exacerbated with the dawn of the mega server consolidation in summer 2011.
Not always. I've played games that do daily restarts as well. It's just that this game needs it. As others have pointed out, they've tried extending the restarts and it causes bad things to happen. Most likely due to how this game isn't very optimized.