Once you reach the top there's much less reason to keep playing. It doesn't have a great way to handle multiplayer situations. It doesn't handle confidence as well as some other systems ie it takes a while to skill test a player.
The biggest issue is fun is not the same fair and its a lot more complicated to tune for fun.
You could, for example, play 100 matches where you were given the closest opponent but at a disadvantage for every single match. There's a lot of other scenarios around how you want to fold in ping based match making and how that smaller pool effects the fairness of the matchhing.
https://en.wikipedia.org/wiki/Elo_rating_system#Practical_is...
Trueskill and many others are often used instead.
https://en.wikipedia.org/wiki/TrueSkill
The biggest issue is fun is not the same fair and its a lot more complicated to tune for fun.
You could, for example, play 100 matches where you were given the closest opponent but at a disadvantage for every single match. There's a lot of other scenarios around how you want to fold in ping based match making and how that smaller pool effects the fairness of the matchhing.