Except they don't use DDR5. LPDDR5 is always soldered. LPDDR5 requires short point-to-point connections to give you good SI at high speeds and low voltages. To get the same with DDR5 DIMMs, you'd have something physically much bigger, with way worse SI, with higher power, and with higher latency. That would be a much worse solution. GDDR is much higher power, the solution would end up bigger. Plus it's useless for system memory so now you need two memory types. LPDDR5 is the only sensible choice.
CAMM2 is new and most of the PC companies aren't using it yet but it's exactly the sort of thing Apple used to be an early adopter of when they wanted to be.
And it's called "CAMM2" because it's not even the first version. Apple could have been working with the other OEMs on this since 2022 and been among the first to adopt it instead of the last:
