5 stars is more just a self achievement for your island, then anything. You would expect it to be where K.K preforms, but that's only at three. Which I think negates the idea of trying to get five stars.
Your villagers won't celebrate like they do on your birthday, all you get is a watering can, and I'll be honest after planting flower, after flower its probably the last thing you would want to see, or be given.
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Islands don't nessesarly have to look sheek, and elegant to get five stars. It just requires a certain amount of decore/items and flowers. I watched this one YouTuber who got a five star island after he placed twenty coffee makers, and a bunch of camp fires on his island. So the whole expectation to make a stunning paradise is kinda misguiding when placing twenty coffee makers, and putting fences on your beach also works.
The game is just coded to give a five star rating once a certain amount of requirements are achieved. Which can be In whatever way your heart desires.
So just keep doing what you’re doing, and you'll get there.