A ring buffer has a limit to the number of unread items before you either block or start discarding. Different use cases I suppose.
If your queue is filling up arbitrarily far, then you are almost certainly in trouble anyway, and want some limitation strategy. The ring buffer gives you this quite naturally.
I suppose there could be cases where you did not want to pre-commit to a buffer size. E.g. you have lots of queues which you expect to be short, but which might grow large in rare cases. But I have never actually seen such a case.
I don't know Erlang or Akka first hand, but I know that Go channels are inpsired by Erlang. Channels can be very numerous and are usually empty; but they are fixed size. In the rare occasion that you think a channel needs more buffering, you must say so explicilty.