I think it's just to stop time travellers from spoiling everything within the first week or so and to keep people talking about the game for months. Unless you time travel (play the game wrong) this stuff shouldn't have a big affect on how you play the game compared with other AC's.
Yea probably some of it is to prevent time travelers from ruining game. I bet some of it also was due fact wasn't complete or completely tested game when launched. Heck look at first event Bunny day was semi disaster. I had so many balloons flying over town it was crazy. They increased rate of regular balloons and then you had bunny balloons that were more frequent than regular added on top... That obviously wasn't play tested too long. Took first day for me to realize this was too much. Also fishing had ton eggs too. I believe they released patch to tone it down.
But I'm all for time travelers not ruining game. Have friend that does that but I don't partake in it. I believe I went to next day a couple times but that's it.