At the start, I obsessively read everything I could on the topics of diabetes and keto. It was a bit exhausting to be honest. I found I increasingly turned to this forum, rather than other resources, because it deals very well with the practicalities of managing T2 rather than endless speculation and opinions as to what causes T2. The low carb and keto advice here is also very practical/sustainable, as opposed to some of the barking mad keto cult stuff you get out on the wider internet. Anyway, I reached my limit when it came to research and trying to answer the questions you've posed, and I've settled on the following:
1) My cells are resistant to insulin and don't absorb it efficiently. Therefore, the glucose being carried by that insulin remains in my bloodstream longer. With more carbs, comes more glucose produced from digesting them. More glucose means more insulin, which as said previously, can't be absorbed efficiently by my cells, so more of it sits there in my blood. A fingerprick test shows how much glucose is sitting in your blood at that precise moment. The longer my red blood cells spend splashing around in that glucose, the more they absorb, and the hba1c shows an average of how much glucose your red blood cells have absorbed over the past 3 months (ish). By eating lower carb, it reduces every one of the previously mentioned factors, but it specifically reduces the amount of insulin my cells need to absorb, reduces the amount of time my red blood cells spend splashing around in the glucose that insulin carries, and therefore my fingerprick test results are lower and my hba1c is lower.
2) Keto is a multi-purpose tool. It pushes carb intake very low and therefore allows better management of all the previously mentioned factors above, e.g. insulin response, glucose. In the context of T2, pushing carb intake very low results in very low glucose levels when digesting food (leaving just the other million or so factors that can influence BG levels to contend with
). For me, keto also reduces appetite significantly and reduces food cravings, which has enabled me to lose a significant amount of weigh, so it's not all just about T2 management for me. Keto works by switching your body's primary energy source from carbs to fat, or more specifically from glucose (produced when carbs are digested) to ketones (produced when fat is processed in the liver). Ketones can then be used by tissues and organs for energy, in the absence of glucose. And how does your body switch between glucose and ketones for energy, I hear you ask? I don't really know, but I'd venture "the magic of evolution for an omnivorous species, who did their evolving in a world without supermarkets and fast food joints".