Shikhar Dhawan was recently named the Man of the Series in the T20I series against Australia and had come off a good T20I series against Windies at home. However, his inability to score even a single fifty on the England tour in any of the international matches and then against the West Indies in the ODI and Tests led to selectors looking for other options at the top of the batting order.
Dhawan has found some purple patch in the shortest format of the game and had hoped that he would be selected for the Australian Test squad. But the selectors had other plans and he was dropped from the squad.
But with Shaw out, Dhawan is probably the aptest replacement for him, as Dhawan bats aggressively and scores run quickly, just like Shaw. Also, Dhawan has no problems with fast bowlers bouncing him and though his numbers aren’t that great in Australia (167 runs in three Tests with highest of 81); it doesn’t mean that he won’t come back from a bad patch, especially after his exploits in the T20I series.