After the flood eating meat is permitted.
It is possible that this is because now that man’s life span was shortened, he would need to develop more rapidly. Another possibility is that now that the continents were divided and the climates would change from season to season, limiting eating to produce would be more difficult. With this allowance, man would be less dependent on food grown from the soil.
Had man remained at his previous, higher level eating meat would have been prohibited. Now that it is permitted it can even be a mitzva (such as eating meat for yom tov).
Once meat has become permitted, the Torah sets limitations to what is permitted. (See the next verse 9:4 which teaches the prohibition of אבר מן החי – eating meat of an animal that was separated from a living animal.)
Later, when the Torah is given to Israel, the only food that is prohibited by the Torah is animal-based food. By contrast all foods that are plant-based are permitted by the Torah. The exceptions (חדש, ערלה and כלאי הכרם) are prohibited for other factors.
Beraishis 9:3
pages 222-223
