the fact no component supplier, not even alibaba sells LPCAMM2 sockets tells you everything you need to know. The only prices I can find are in $30 range per socket

Connectors are expensive, high-speed ones particularly. $30 is fine, though it makes a giant difference at what quantity that is. Did you look at a single one or 1k?

Honestly, reasonable.

I've been eyeing LPCAMM2 interposers for non-RAM uses - as an off the shelf connector for stacked PCB designs. The conclusion was that it wasn't produced or used at sufficient scale for it to work.