The best-intentioned witnesses don't always give 100% accurate testimony. If there is other evidence (ie. pictures) that seems to show convincingly otherwise (there was an IV or other simple reason), the defense probably isn't going to argue.
What would be the point? Remember, the defense here is that there is a murder conspiracy and an effort to frame KR. Would the defense now be trying to convince the jurors that random doctors are in on it? At some point it would pass into a level of absurdity and could likely hurt KR's chances.
The defense has to pick and choose their battles, wisely.
Along those lines, here are a couple of examples from the first trial that I didn't think helped the defense. I don't know if they have or will go back down these roads, but I'd be curious...
1) Trying to imply Colin Albert could've done it. I think this isn't allowed in the new trial, but I thought it looked bad for the original defense.
2) The plow driver. Not only did his testimony seem dubious, at best, but it also didn't seem to fit other conspiracy narratives.