What are reasons to reject a literal and historical take on Noah's Flood?
Quite simply, it is incredible (in the literal sense meaning 'not rational to credit') that such an event could occur and not leave substantial evidence.
What sort of evidence would we expect to see if Noah's Flood was real? Well, the same sort of evidence as of local flooding, but on a much greater scale. For instance, we might find organisms buried in mud or topological reshaping.
...which is exactly what we do see. If we are going to reject the Flood, we need an alternate explanation. Therefore, the correct question is "why is the enormous body of evidence not believed to be evidence of Noah's Flood?"
The answer to this is two-fold, but essentially boils down to Uniformitarianism, a worldview that was pioneered predominantly by Charles Lyell, and "deep time" (i.e. "old Earth"). Originally, Uniformitarianism was the view that Earth was shaped by the same processes observed in continuous action. For example, the Colarado river is very slowly continuing to erode the Grand Canyon. By extrapolating the current rate of erosion, one can estimate how long it would take the canyon to form assuming the rate of erosion is constant. Based on such measurements, many geological features are claimed to require many thousands or even millions of years to form.
We now know, however, that Catastrophism is a better overall model. First, we have many evidences of processes supposedly requiring great lengths of time happening extremely quickly (in days or weeks, sometimes even in hours or less). Second, there are many processes which, even under Uniformitarian assumptions, result in maximum time limits less than tens of thousands of years.
There remain three primary lines of evidence that suggest "deep time".
First, nearly everyone agrees that stars are really far away (billions of light years). According to our current models, we have no explanation of how their light could have reached us given such distances. However, there is a lot we don't know about cosmology. In particular, the cosmic microwave background is too uniform according to our current models. From a position of philosophical naturalism (that is, denying a prior that anything supernatural exists and not allowing miracles), it is extremely hard to conceive of how distant stars can be visible if they haven't been around for a really, really long time. From a Christian perspective, however, given the obvious incompleteness of our models, this line of evidence would seem inconclusive.
Second, we are highly confident that significant amounts of radioactive decay has occurred. While it's possible God Created rocks that "look old", most Creationists reject this explanation. Again using Uniformitarian principles, such decay can be extrapolated as an indication of the passage of very long lengths of time. However, this is riddled with assumptions and ignores significant evidence that accelerated decay has occurred. (Conversely, accelerated decay would produce a substantial amount of heat, and no good explanation for what happened to all this heat has yet been proposed.)
Third, humans are believed to be descended, along with (almost?) all other existing life, from some single ancestral organism. No credible explanation for how this could occur in a "short" (thousands of years) period of time is available or seems possible. Of course, this belief ignores all sorts of problems... because the alternative is anathema.
What are reasons to reject a literal and historical take on Noah's Flood?
We've shown above how a "scientific" case against the Flood can be made, but the arguments all have one thing in common: they presuppose that God does not exist, and that miracles cannot occur. They also ignore all manner of inconvenient evidence that shows the resulting worldview to be false.
Paul writes (in Romans 1:20), "For [God's] invisible attributes, namely, His eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made." The evidence in favor of Noah's Flood is overwhelming. It requires an a priori commitment to rejecting God to build a case against it.
Sadly, because there is so much pressure to accept such counter-Scriptural claims, many people who are otherwise Christian have given in and tried to make an accommodation for such beliefs.
What are reasons to reject a literal and historical take on Noah's Flood?
Scripture teaches that humans are sinners. We are in a state of rebellion, with many opposed to God. We love the works of darkness and do everything possible to reject God's righteous judgment.
2 Peter 3 warns "that scoffers will come in the last days with scoffing, following their own sinful desires. They will say, 'Where is the promise of his coming? For ever since the fathers fell asleep, all things are continuing as they were from the beginning of creation.' For they deliberately overlook this fact, that the heavens existed long ago, and the earth was formed out of water and through water by the word of God, and that by means of these the world that then existed was deluged with water and perished." 2 Thessalonians 2 tells us that "those who are perishing [...] refused to love the truth and so be saved. Therefore God sends them a strong delusion, so that they may believe what is false."
Ultimately, the answer to the question "what are reasons to reject a literal and historical take on Noah's Flood?" is "because it shows that God exists". If God exists, He Created us. If He Created, He has dominion. If He has dominion, we are responsible, and will answer, for our actions.