Australia is a tough country to conquer, for batsmen and bowlers alike. On the face of it, the pitches there are more conducive to faster bowlers with the extra pace and bounce they provide, but in reality it's not that simple. We saw how the Indian bowlers struggled in the first couple of ODIs, in Sydney, and the extra bounce that was supposedly their ally was actually adding to their problems. The new batch of white Kookaburra balls don't swing at all in the air, and if there's no sideways movement off the surface, which there wasn't in Sydney, the bounce makes the ball sit up quite nicely to get hit.
The same is true for the spinners - the grass on the surface makes it tougher for the older white ball to grip and turn. If the ball neither turns nor stops on the surface, there's precious little a bowler can do to rein in the batsman. More so if you're still figuring out the right pace to bowl at and searching for the appropriate length for that particular surface.
Fast bowlers are always advised to bowl the length that ensures the ball hits the top of off stump. When you bowl that line and length, you create difficulties for the batsman. But the fact is, that length varies from one surface to the other. While in India you have to bowl a certain length to hit the top of the stumps, in Australia that length is a lot fuller because of the bounce. In theory, the difference of a couple of feet isn't much; every bowler bowls shorter and fuller every now and then intentionally anyway. But in practice, the difference is a lot more difficult to conquer: changing the length for a couple of deliveries is not challenging, but changing the length of the stock ball requires extensive training - you're developing new muscle memory.
Jasprit Bumrah is India's lead white-ball bowler, and his discomfort in getting used to the demands of a new pitch was visible in the first two games. He started by bowling the stock ball but found no venom in it, for the bounce was comfortably taking the ball over the stumps.
Australian batsmen have grown up playing on these surfaces, so their response was very different from whatever the Indian batsmen were doing in the practice sessions leading up to the game. Of course, the pitches provided in the camp are vastly different from those for international cricket. Bumrah tried bowling a little fuller, but the lack of swing and seam allowed the Australian batsmen to play on the up and through the line, which is something you can do on pitches with true bounce and pace.
"Chahal's dilemma about the right speed and length to bowl at was evident, and the fact that the Australian batsmen were on top didn't help his cause. It didn't give him any time to settle into a rhythm"
Also, the response mechanism of a bowler every time a batsman reacts to a ball is inbuilt by the time he reaches the international arena. Bumrah dug in short, it went over the batsman's head; a little fuller than that allowed the batsmen to swivel and play the pull. Now, learning on the job is fine, but there's the matter of controlling the spillage of runs, and finding that balance isn't easy. It's like fixing a mechanical error in a car's engine while the vehicle is on the move.
Things were equally challenging for Yuzvendra Chahal and Ravindra Jadeja. While Jadeja's style of bowling doesn't change much from surface to surface (which is why he struggled less), Chahal's response varies quite a bit from one surface to the other. His craft is based on creating enough confusion in the batsman's mind by varying the pace and using whatever little purchase is available off the surface.
The thumb rule for spin bowling is to increase speed while bowling on spin-friendly pitches and to bowl slower on flatter surfaces. Chahal needed to find the right pace to bowl on the Sydney pitch. He went a few miles slower a lot of times but the lack of assistance offered by the surface made it easier for the batsman to manoeuvre. The problem with going too slow is that it allows the batsman to go deep inside the crease, even to the deliveries that aren't very short. When that starts happening, you as a bowler try to push the ball fuller without quite realising that you are going to be landing the ball virtually at the batsman's feet.
Chahal's dilemma about the right speed and length to bowl at was evident, and the fact that the Australian batsmen were on top didn't help his cause. It didn't give him any time to settle into a rhythm. The pitch in Sydney was so true that you could play even the spinner on the rise - something that you avoid attempting if there's the slightest bit of help in the surface for spinners.
Playing on Australian pitches can be extremely intimidating, especially for batsmen from the subcontinent, but still the consensus is that they can be the most batsman-friendly surfaces in the world too. Once the initial challenge of adjustment is taken care of, the true nature of the pitches makes for consistent strokeplay.
Picture it from a bowler's point of view: it's only a small window of opportunity for them to make inroads and, if they fail to do so, their challenges increase manifold.