Why doesn't every wizard duel with Expelliarmus?

In the Harry Potter universe disarming your opponent seems to be the most logical opening move in a duel, but only Harry seems to do this often. Is there any in universe explanation for this, for example an Expelliarmus counter spell?

I can understand why you might go for Avada Kedavra if you wanted to kill someone as quickly as possible and were prepared to use it, but many duels seem to last for several spell exchanges that could be avoided if you just disarmed your opponent.