@Naomi141 The more stays you host, the less likely it is that you'll have a completely unblemished star rating, that's true. But on the other hand, every new rating lessens the impact that a subsequent rating will have on your average.
There is a case to be made for phasing out old reviews after a certain amount of time has passed. No home is the same today as it was 5 years ago, so the relevance of a review is proportional to how recent it is. But I think there would be a huge outcry from hosts if their old ratings dropped out of the average, because then they'd lose their firewall against the impact of a single low rating.
I doubt there are many guests out there who would only consider booking a place that has 100% 5 star ratings. That would be like refusing to see a movie unless it has a 100% on Rotten Tomatoes. Absolute perfection is a worthy goal in some professions - you wouldn't want to fly with a pilot who only landed the plane 99% of the time - but it doesn't map onto the spirit of hospitality. If you'd told me 20 years ago that one day people would be giving star ratings to other people's houses, I'd have thought you were looney tunes.