If the universe provides crystal-clear evidence of design [...]
Let's start with that "if".
Paul is quite clear that there is no "if". "What can be known about God is plain to [the unrighteous], because God has shown it to them. 20For his 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. So they are without excuse." (Romans 1:19-20)
"The heavens declare the glory of God." (Psalm 19:1) All around us is clear evidence that Creation has a Creator. "Common Descent", which at heart is a rejection of the Creator, is contradicted by mathematical models, by historical evidence, and by ongoing observation. Abiogenesis is in a similar boat. When it comes to cosmology, one atheist stated that "if none of us knew in advance that stars exist, front line research would offer plenty of convincing reasons why stars could never form". Nor has such formation ever been observed, nor is the belief in non-miraculous star formation consistent with observations.
Geology and local astronomy are also chock full of evidences that Earth and its local neighborhood are not millions of years old, much less billions.
In short, all of nature, but especially biology, point to a Designer.
how is it that physicists, who study the fundamental laws underlying everything, and biologists, who deal constantly with the complexity of biology, largely fail to believe in a designer God? How is it that something supposedly so obvious turns out not to be obvious for the vast majority of scientists?
In fact, many studies have suggested that disbelief is not nearly so widespread as the cited studies would suggest. There's also a strong political incentive toward atheism, or at least to keeping one's beliefs private. (See for example The Altenberg 16.) Even so, there are surely enough unbelievers as to require an explanation.
...And once again, Paul has answers: "For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth." (Romans 1:18) "They became futile in their thinking, and their foolish hearts were darkened. 22Claiming to be wise, they became fools". (Romans 1:21-22) Why? Because "people loved the darkness rather than the light because their works were evil". (John 3:19) Scripture warns what that, for these people, "God sends them a strong delusion, so that they may believe what is false". (2 Thessalonians 2:11)
It's human nature to flee from accountability, but it's self-evident that we, as Creations, would be accountable to our Creator. Moreover, knowledge of our shortcomings is "written on our hearts". We know, deep down, that we're broken, but many people are in denial. That denial can only be reinforced by denying God as well, and so that's exactly what many people do, and what God helps them do so that, when they are called to account, they will be "without excuse".
If you look into it, you'll find that this reasoning is clear. Modern "science" "accept[s] scientific claims that are against common sense [...] in spite of the patent absurdity of some of its constructs, in spite of its failure to fulfill many of its extravagant promises of health and life, in spite of the tolerance of the scientific community for unsubstantiated just-so stories". Why? "Because we have a prior commitment, a commitment to materialism [...] not [because] the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but, on the contrary, [because] we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counter-intuitive, no matter how mystifying to the uninitiated [...] for we cannot allow a Divine Foot in the door." (Lewonski) Indeed, the goal of modern "science" is to "free the science from Moses" (Lyell). These claims are not about finding the truth, but about rejecting God and rejecting the history of Scripture.
Scripture clearly tells us why men do this, what we ought to think of them, and even specifically predicts such denials. "They deliberately overlook this fact, that [...] the earth was formed out of water and through water by the word of God, 6and that by means of these the world that then existed was deluged with water and perished." (2 Peter 3:5-6)
