After Hashem saw the Korban of Noach, He decided that from now on, the world can continue to exist, and without another Mabul. Why now? Chazal say that the reason why Noach brought the Korban was because he was grateful; i.e., that he was saved from Mabul and the “prison” of the Teiva. We can suggest that as soon as Hashem sees thankfulness, then things can keep moving in this world.
The whole Tzara of Dor HaMabul was: כִּי מָלְאָה הָאָרֶץ חָמָס theft. חָמָס Theft is the symbol of dissatisfaction. When you desire what isn’t yours, it’s a sign that you aren’t spending time and Kochos to count your blessings. Dissatisfaction is the first step to all evil and eventual destruction.
Although Noach was surely always a Sameach B'chelko (and his very name means “Menucha” and not looking for trouble) yet, bringing a Korban is an official major gesture of gratitude, like saying Nishmas or bringing Bikkurim. I would suggest that periodically it would be K'dai (worthwhile) for every person to make an official thank-you Matzav, which is actually the idea of all our Yamim Tovim.
The very existence of a Yid is being a thankful human, since “Yehudi” means “Thank you” (and the name is the description and the essence of the person). We thank constantly, and therefore our daily Tefilos are loaded with “thank you” and Haleluka’s. And once in a while, we go all-out with Hakaras HaTov; i.e., by Yamim Tovim and Korbanos, and special Seudos Hoda'ah, etc.
