That RAM costs both in terms of space and power/heat. Especially high-speed cache RAM. That would make the SoCs huge and expensive for no particularly good reas

That RAM costs both in terms of space and power/heat. Especially high-speed cache RAM. That would make the SoCs huge and expensive for no particularly good reasons. Also large caches need a lot of logic to ensure coherency between multiple cores - with a small cache the probability of conflict isn't that big, so you can afford to keep it simple. With a huge cache such conflicts between cores would be pretty much assured and you would have to dedicate a lot of silicon just for managing access.