First test as the captain for Cummins. Let's see how it goes from here for him. England was perhaps a bit overconfident? They didn't played any warmup matches before the first test. The only match practice they had before the Brisbane test was the abandoned match between their A and B teams, which lasted for just 29 overs (two and half days out of three days washed out). Increasing number of COVID cases in Australia (as well as the ongoing BBL) means that they can't yet schedule any matches against the first class teams.
Now it's too late to discuss the warmup matches and why England did not opt for them. I do think that the England team, after this loss, will come back strong in the second test. They have the players and talent to turn the tables, therefore Australians can't relax and take things for granted even though they have won the first match.