To the OP, curious a) what mileage currency you were burning, and b) if you're a CX elite?

I *suspect* you weren't booked on the earlier flight because it was full/almost full.

I am certain CX prioritizes certain pax for rebooking, seen it with my own eyes a number of times. Not just for elites, but for infrequent pax who pay cash. CX logic isn't "you're the F pax, I prioritize you over the rest." Not trying to get into a debate here, just saying that's not how they work.

This probably doesn't make it feel any better to the OP, but have numerous anecdotes both myself and some colleagues/friends to think this is how it happens. I would guess two unconnected award tix aren't the highest priority for CX, especially if non elite (lower) and using a non-CX currency (least). Even then, CX still does a fairly good job IMO with issues like thos, even if you're not their #1 priority.

It sounds like you were reasonably accomodated, just they didn't give you the five star service you might've expected as a flying "F pax". But on the flipside, CX earns itself a great deal of loyalty from high cash spenders with a reputation for coming through exceptionally well during problems, even if maybe they're flying J or whatnot. If you are looking for anecdotes PM me.