As an outsider the time does looks right. Although Ganguly has contributed hugely to Indian cricket and World cricket.
It seems to me he has become a problem. There are batsmen who are ready to replace him and there is a new coach and capitain. Sometimes a decision has to be made and one can't always wait for the right moment. It also makes it clear to the other players a new era is here and new opportunities.
"I come to bury Ceaser not to praise him"

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"Checkout the big brain on Brett" Pulp Fiction