There was a trend for a while of making business/power laptops much more configurable (I have an old Dell with a hard drive cage that swaps out without removing

There was a trend for a while of making business/power laptops much more configurable (I have an old Dell with a hard drive cage that swaps out without removing any screws). But most laptops are more about form rather than function; their design requires reworking all the internals to prevent getting a big clunky heavy box that overheats. For very low-power machines you might have tons of internal space free, but more powerful laptops need complex heat management in addition to reducing size and weight. It's only now that we have very advanced fabrication techniques and energy-saving designs that we no longer have to hyper-focus on heat exchange. If size and heat and weight weren't a factor, you can bet that a standard would have arose to manage interchanging parts. But soldered ram is a good example of why that's just not necessary, and can be counter-productive for reducing cost and maximizing form factor.