The real reason so many laptops have moved to soldered RAM
The main two reasons I could think about from all the strategic decision-making to using soldered RAM or socket RAM are the thermals, the efficiency, and the form factor
Not only are soldered modules much thinner, but rumor has it that they’re also easier to put together. With a RAM slot and a memory stick, you’d need an engineer to work on each laptop as it comes off the assembly line. Soldered parts don’t need that much human supervision and can be produced entirely by machines. Let’s not forget that they’re cheaper all on their own, without even considering the manpower required — they use fewer parts.