The two superpowers of cricket clash, but there can be only one World Champion.
A number of excuses have been offered for India's loss:
Politics/match fixing - the dejected looks and behaviour of the Indian players shows that these are not men who intentionally lost.
The toss -Cummins surprised almost everyone when he chose to field; if Indian captain had won toss he would have chosen to bat, so no matter the result of toss India would open the batting, so the toss had no effect on match.
That India had won ten matches in a row, and was therefore due for a loss. Australia won eight matches in a row leading up to the final, so not much difference.
Some comments:
The Indian cricket authorities prepared the pitch for this match; they chose to make it slow believing this would help Indian side and disadvantage the Australians. This trap backfired, as Australia handled the conditions better.
Smith was given out LBW, and surprisingly didn't challenge the decision, if he had he would have stayed in. Later in the match his good friend Labuschagne was given a not out LBW decision that India challenged, and result was umpire's decision, so he stayed. If the umpire had originally given an LBW, Labuschagne would have been gone (too late to save India). So this was a balance.
It was the Travis Head show - two teams enter the Travisdome, only one team leaves victorious.
Negative fielding by India, they should have had men in slips positions.
There are claims that India was the better team (and therefore should automatically have won), but this match was to determine who was the better team, and it was not India. Earlier in the year (June) Australia won the World Test Cricket Championship final (also against India).