Why didn't Mitchell's defence raise this in court?
Because it would've been absolutely futile to do so. The DNA in this case can't move any debate forward; it was neutral as no incriminating DNA was ever found at the locus or anywhere else, and hence why an agreement was made between defence & prosecution not to use or discuss the DNA.
The only one full profile that was found in this case was a tiny semen stain from SK on the t-shirt that Jodi wore that evening. It was explained scientifically at court that said semen stain got on that t-shirt innocently; the t-shirt actually belonged to JanineJ and Jodi had borrowed it that evening, and, unbeknownst to her, it had a degraded semen stain on it -- a semen stain that had survived a washing machine cycle (the t-shirt had been freshly laundered, but, because SK & JanineJ were in an intimate relationship, semen from a previous sexual encounter between the courting, intimate couple found its way onto that t-shirt and survived a washing machine cycle and then Jodi borrowed it. This was all explained carefully & scientifically in court and it was accepted. It was accepted as 'innocent transfer'. As regards semen being found on Jodi's body, etc, well, that too got there innocently and was accepted in court; the rain had diffused the degraded semen stain from SK across Jodi's body (ie, traces of semen had migrated from one place on Jodi's body to another). What's also worth considering is the fact that where Jodi was murdered and where her body lay was a popular place for youths to congregate, smoke, drink alcohol and have sex -- so it stands to reason there would have been used condoms and traces of semen from previous sexual encounters between youths and these traces would have innocently got onto Jodi's body (ie, 'innocent transfer'). The crux of the matter is that there was no incriminating DNA found at the locus (ie clumps of hair from an assailant, an assailant's blood or and no fresh.semen found); it was all partial profiles and inconclusive results from degraded dna that got there innocently. If there was fresh dna at the locus it woukd have been detected as the forensic equipment used in this investigation back in 2003/04 was state-of-the art that could pick up the smallest of traces of DNA (and the rainfall on 01.07.03 would not have been able to completely wash away all traces of DNA). There was nothing found. Besides, the pathology report confirmed that Jodi had't been raped. So, again, nothing incriminating was found forensically to take the case forward, and certainly nothing to suggest it was a stranger who did it.
What are we left with? Any logical thinker would be able to deduce that LM got rid of his german army parka and shirt because they likely had traces of Jodi's blood on it (and many people, including school teachers and best friend David High, said LM owned these items of clothing prior to the murder on 30.06.03). Why did he and Corinne deny he ever had the German parka jacket & shirt prior to 30.06.03, when so many peoole said under oath he did have both prior to the murder? And why did LM buy the exact same jacket and shirt as the ones in question, on 08.07.03? It's a rhetorical question, obviously. We all know why. He's guilty as hell.