So what if we use our experiences and in-depth knowledge of a past protocol, take into account the flaws, and build something better? You say "re-implemented TCP" as if it's the only possible way to build a reliable packet protocol, and that it has no flaws, and we can't make any improvements to it.

TCP isn't alien technology we don't understand. We do understand it, and its limits, and its constraints, and that means we can build a better one next time.