The ZX80/81 16K RAM pack used two PCBs joined with a connector in the middle.
I'd initially assumed this was due to reuse of the original 3K RAM pack case (which has a single PCB and uses static ram) for ZX80 16K RAM packs and then the same case being used for the ZX81, however the case is significantly different and I think there wasn't enough space inside the older design.
I can't figure out why Sinclair didn't create a RAM pack with physical packaging similar to the Memotech design. A single PCB should be more reliable and the additional plastic cost of a wider case can't have been that much.
I remember there was an initial shortage of 16K RAM packs at the ZX81 launch, I originally ordered a ZX80 and received my ZX81 before the magazine reviews arrived but had to wait several months for a RAM pack, which leaves me wondering if there was some manufacturing issue.
Is there some piece of Sinclair history or electronic reason I'm unaware of?