The standard overhead join goes back to a time when almost all flights were non-radio. The signal square gave the required information which could be given in no other way. Hence overhead above circuit height to read it and descend etc..
There is still alot of non radio flying, more I suspect than many realise, and long may it continue. It really is the best way to fly and far more enjoyable. A good case can be made that it is safer too; but I won't go there.