She was also charged with a number of other deaths which they couldn’t convict her on. On similar (poor, IMO) evidence.
Competing medical evidence / other explanations for the deaths weren’t presented at trial because only one expert (in the entire UK) was prepared to risk being blackballed by the NHS to represent the defence. And in the end, for whatever reason (incompetence, a tactical plan that failed or whatever else) her defence chose not to put him on the stand.
Subsequently, MANY expert pathologists and doctors, worldwide, have come forward and expressed doubts about the way the deaths were represented in court, how the statistics were interpreted and other aspects of the prosecution case.
The jury are just ordinary men and women. If a reputed ‘expert’ takes the stand for the prosecution (and that’s the only interpretation they hear) then they’re much more likely to convict than not. There’s a big problem in this country with medical witnesses. They know that if they become known as defence experts they’ll be actively ostracised by the wider NHS.