[ribit]

The beauty and success of DIMM modules is that they are a simple slide-in to install technology. It's easy to operate, cheap, robust, and it is very space efficient. Imagine RAM modules in an LGA socket instead... how much space would it require? How robust would it be? What will be the price? I am quite sure all of these issues can be solved, but is it worth it? Let's be honest, users who are interested in having upgradeable RAM in their ultraportable laptop are such a small minority that the practical interest in developing modular low-powered RAM is close to zero.

[formerly_proven]

The practical interest might be close to zero because in the past memory upgrades a number of years down the road were one of the most common upgrades and added tremendous value and another few years of life. Similarly many older laptops got a second life by being upgraded to SSDs. Accidents like that, which prevent sales of new units, can't happen if storage and memory are soldered on.

I don't think this is the driver of these decisions per se, but it is undeniably a bonus for the manufacturer; non-upgradable devices become obsolete faster, necessitating new replacements.

[codedokode]

Also even when RAM was replaceable, many manufacturers put low limits on its size, I guess for the same purpose.

[Stratoscope]

I don't know about other brands, but for ThinkPads (both in the IBM and Lenovo eras), there was often a stated maximum RAM that was based only on the capacity of SODIMMs available at the time of manufacture.

But it wasn't an artificial limitation. In practice, once larger capacity memory became available with the same technology and form factor, it would work fine. I have upgraded several ThinkPads with memory beyond what the original datasheets said was possible.