Comment by jraph

I don't think the question would make much sense. Why did Apple do X and not Y (unrelated to X) is not an interesting question. It would seem close to whataboutism. They were willing to spend money on X. They are not willing to spend money on Y. Or, they didn't think about doing Y. Or, they needed X. They haven't needed Y. Apple want fast VMs and also they haven't needed Btrfs. What insight can you get? There's no relation between the two. You'd get the same insight by asking "Why didn't Apple implement Btrfs?", but by linking the two in the same question, you are kinda implying there's a link.

But the question would have been highly relevant had Apple developed a new FS, and disk images and FS do seem related at first. I didn't want to assume whataboutism, so I figured OP was possibly confused because this is likely, and I wanted to give them a hint without bluntly asking whether they confused things. I could have, really there's no harm in being confused, nor in asking whether someone was confused.