Cancer cells may favor glycolysis to lactate for building blocks over ATP production.

“Our cells can turn glucose into something called pyruvate and that occurs outside of the mitochondria and that's not a highly energy efficient process it doesn't generate much ATP you then have a decision to make as a cell which is basically how quickly does the body want ATP and as a general rule when it wants it quickly it's an anaerobic environment if you think about things that drive quick ATP requirement and so then it will just say look we'll just turn this pyruvate into lactate that's a glycolytic pathway which is not particularly efficient either it doesn't generate that much more ATP but it has the luxury of saying I can guarantee to do this quickly and I don't need to be limited by cellular oxygen”

“hey it might not be that the mitochondria of the cancer cells are defective and can't undergo oxidative phosphorylation it might be that they're optimizing for growth as opposed to metabolism they don't care as much about ATP as they care about building blocks and therefore they're deliberately taking an inefficient route of glycolysis to lactate because they want the cellular building blocks”