I have read (from a powered aircraft point of view) that the circuit is a busy time for the pilot(s), I don't know if it is the same for gliding but I can certainly understand why it is a training priority.
When gliding you have to assume that
- none of the other aircraft have a radio
- the club's launchpoint radio is irrelevant because might or might not be on, and in any case they almost certainly can't give you instructions
- there are often other gliders in the circuit too, they might well "pinch your piece of grass", and you'll have to decide to land somewhere else
- there's no such thing as a standard circuit: the circuit is modified according to whether lift/sink is encountered
so, yes, it can get busy and training does address the issues
As an example, at my club I've watched three gliders land abreast of each other within a few seconds; at a pinch another two could have done it as well!
(And that's not considering competitions, where there can be up to three movements per minute as they launch all (~50) gliders within an hour.)