Rubbish. When does a bus get to 11000m, and how often does a Sydney team have to sleep not in their own bed. Plus if it was easier, why wouldn't teams fly on game day?
I think you are underestimating it slightly.
For starters, they have to get to the team bus that would then take the brisbane side to the airport.
They get a flight to sydney (quicker than driving from the CBD to penrith)
They then have to get a bus from the airport to where ever they are playing.
Teams do occasionally fly from say Sydney to Canberra or Newcastle to Canberra, but most of the time they get the bus because its fucking heaps cheaper and flying from sydney to canberra is not actually that much faster driving (when you take into account getting luggage and busses to and from the airport etc)