I have never understood why this case hasn't been solved by DNA
because the minuscule amount of "unidentified" DNA that was supposedly found in JonBenét's underwear wasn't significant enough of a presence to be able to tell anything about who it may belong to. the only thing that could be conclusively deduced about it was that it was human. basically, DNA tests were inconclusive because not enough "complete" DNA strands were present to properly tell whether the DNA was even
male or female, let alone even more in-depth details. a stranger who molested and murdered a little girl within the past 24 hours of her autopsy would have left a lot more DNA than was found on JonBenét's underwear, especially considering this crime scene wasn't exactly the work of a seasoned criminal who might know how to disguise their biological footprint.
the package this pair of underwear came from was recently opened, if I remember correctly, as they had been bought as a gift or something right around that time, and years later, the "foreign" DNA was studied again with newer technology and it became clear it was likely trace amounts of DNA from factory workers who manufactured the underwear before JonBenét even owned them, if it were a stranger's DNA on there at all. testing a pair of brand new underwear fresh out of a package without having been touched by anyone in the sterile laboratory revealed that trace amounts of human DNA — the same, minuscule amount found on JonBenét's underwear that was unable to give conclusive details — were still found.
so, if no one that wasn't in the house left their DNA on JonBenét, that means no one was there that night who wasn't supposed to be there. DNA evidence can't solve this case because you can't expect a parent not to have physical contact with their young daughter who still needs help getting dressed, bathed, changed after bed-wetting, etc. or her items, so you need to find other evidence that would be incriminating.
long story short, this case didn't
have any DNA that wasn't expected to be there. circumstantial evidence was necessary to solve JonBenét's death, but the media (and the Ramseys) stirred the sensation pot and cranked the rumor mill enough that circumstantial evidence and public opinion became muddled and solving the case in a satisfactory manner became pretty much impossible, because everybody developed a strong bias either towards or against the family. you can't charge someone with murder in cases of circumstantial evidence when 50% of a jury think they did it and another 50% think they didn't do it. "innocent until proven guilty" is a hallmark of criminal justice pretty much everyone has heard.
if any person in that house was found guilty, John and Patsy would both come under serious fire — either because one or both killed JonBenét and then covered it up together, or because Burke (who was a minor at the time and therefore couldn't be and wouldn't be tried the same way) accidentally hurt her and then John and Patsy finished the job and covered it up together. both of which are very, very illegal, obviously... the sentence both Ramsey parents would have been given wasn't a slap on the wrist — they would have been doing significant time, for one reason or the other. that would leave Burke with parents in prison and a dead little sister, and not even the court of law is willing to do that without 100% proof positive evidence, which wasn't obtained due to a botched crime scene and swayed investigation due to media frenzy.
(hope this was a clear response, I'm in a bit of a rush right now but wanted to respond with some of my thoughts! c: )