Yeah, that makes sense now. I think, personally, I've simply seen that design around a bunch, but great on you to question it and call it out -- also plausible that my own headcanon doesn't check out.
Also for what it's worth, I can guess what some of the answers might be. For example, it's possible you'd need very precise timing facilities that aren't always available, in order to be able to guarantee high throughput with correctness (like Google Spanner's). Or it might be that doing so requires a trade-off between availability and partition-tolerance that in some applications isn't justified. But I'm curious what the answer actually is, rather than just (semi-)random guesses as to what it could be.