There are specific performance benefits to soldering your memory to the board or making them part of the main die itself. It’s why GPUs have been doing it for a long time, and why laptops with soldered ram can often achieve higher clocks and lower latency than their socketed counterparts. It’s a tradeoff, but a calculated one. I’m sure Apple also adds the extra revenue from absurd upgrade costs into their calculations.

Somebody has never been to a top fuel drag race. Impressive does not even begin to describe what those “fast cars that can only go straight” are capable of.