Comment by ryanschaefer

In large enough systems, it becomes prohibitively expensive to keep consensus of the state of all members.

Sure with 10 or so hosts it’s trivial to select the least busy one but at the scale of 1000s of hosts you begin to run into a ton overhead just to decide where to forward a request.

As many others have said, O(N) for each request vs O(1) while avoiding hot spots.