You yourself mention the trade off — the „sardine class“ is a six-people per cabin couchette (60 ppl per railcar). The private class is luxury (10-17 cabins per railcar).

We got 65 private pods or close to 40 little single cabins - in a refurbished railcar. In a new car it would be more.

We put together some explanation of the economics and the difference between old and new cars: https://luna-rail.com/approach