For me, it's pretty obvious that rating is arbitrary and depends on how optimistic/perfectionist/obsessive/etc. the reviewer is and that there is not much difference between 4 or 5 stars.
It's not users, it's the platform itself. AirBnB and other companies like Uber and Lyft will significantly deprioritize you if your average rating isn't very close to 5 stars. Rating your Uber driver 3 stars can significantly affect how many fares they're offered and therefore how much money they can make.
But if users don't care, why do platforms care? Maybe it's actually a reliable signal?
Obviously it's also more reliable in the context of other evaluations by the same reviewer which the platform has easy access to, i.e. if someone always gives 5 stars, then a 4 star review from him is much worse than one from someone who never gives 5 stars.
Users caring might mean that a user is 15% more likely to select a 5 star host over a 4.5 star host, not that the user will say a 5 star rating is a top concern.
For me, it's pretty obvious that rating is arbitrary and depends on how optimistic/perfectionist/obsessive/etc. the reviewer is and that there is not much difference between 4 or 5 stars.