A 30% larger die going from 16 billion to 20 billion transistors on TSMC’s latest and greatest is only $30 extra? Where did you get those pricing figures?8GB of LPDDR5X and a 30% larger die might each cost $30 extra. Most people are smart enough to go for 16GB and/or 512GB, so the margins are definitely still there.
There are plenty of ultraportables like ThinkPad T14s with 32GB RAM. Most people look at the overall package and not the memory technology.